linux/mm/mmu_gather.c

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#include <linux/gfp.h>
#include <linux/highmem.h>
#include <linux/kernel.h>
#include <linux/mmdebug.h>
#include <linux/mm_types.h>
#include <linux/mm_inline.h>
#include <linux/pagemap.h>
#include <linux/rcupdate.h>
#include <linux/smp.h>
#include <linux/swap.h>
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
#include <linux/rmap.h>
#include <asm/pgalloc.h>
#include <asm/tlb.h>
#ifndef CONFIG_MMU_GATHER_NO_GATHER
static bool tlb_next_batch(struct mmu_gather *tlb)
{
struct mmu_gather_batch *batch;
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
/* Limit batching if we have delayed rmaps pending */
if (tlb->delayed_rmap && tlb->active != &tlb->local)
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
return false;
batch = tlb->active;
if (batch->next) {
tlb->active = batch->next;
return true;
}
if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
return false;
batch = (void *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
if (!batch)
return false;
tlb->batch_count++;
batch->next = NULL;
batch->nr = 0;
batch->max = MAX_GATHER_BATCH;
tlb->active->next = batch;
tlb->active = batch;
return true;
}
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
#ifdef CONFIG_SMP
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
static void tlb_flush_rmap_batch(struct mmu_gather_batch *batch, struct vm_area_struct *vma)
{
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
struct encoded_page **pages = batch->encoded_pages;
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
for (int i = 0; i < batch->nr; i++) {
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
struct encoded_page *enc = pages[i];
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
mm/mmu_gather: define ENCODED_PAGE_FLAG_DELAY_RMAP Nowadays, encoded pages are only used in mmu_gather handling. Let's update the documentation, and define ENCODED_PAGE_BIT_DELAY_RMAP. While at it, rename ENCODE_PAGE_BITS to ENCODED_PAGE_BITS. If encoded page pointers would ever be used in other context again, we'd likely want to change the defines to reflect their context (e.g., ENCODED_PAGE_FLAG_MMU_GATHER_DELAY_RMAP). For now, let's keep it simple. This is a preparation for using the remaining spare bit to indicate that the next item in an array of encoded pages is a "nr_pages" argument and not an encoded page. Link: https://lkml.kernel.org/r/20240214204435.167852-7-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:31 +00:00
if (encoded_page_flags(enc) & ENCODED_PAGE_BIT_DELAY_RMAP) {
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
struct page *page = encoded_page_ptr(enc);
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
unsigned int nr_pages = 1;
if (unlikely(encoded_page_flags(enc) &
ENCODED_PAGE_BIT_NR_PAGES_NEXT))
nr_pages = encoded_nr_pages(pages[++i]);
folio_remove_rmap_ptes(page_folio(page), page, nr_pages,
vma);
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
}
}
}
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
/**
* tlb_flush_rmaps - do pending rmap removals after we have flushed the TLB
* @tlb: the current mmu_gather
* @vma: The memory area from which the pages are being removed.
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
*
* Note that because of how tlb_next_batch() above works, we will
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
* never start multiple new batches with pending delayed rmaps, so
* we only need to walk through the current active batch and the
* original local one.
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
*/
void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma)
{
if (!tlb->delayed_rmap)
return;
mm: mmu_gather: allow more than one batch of delayed rmaps Commit 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") limited the page batching for the mmu gather operation when a dirty shared page needed to delay rmap removal until after the TLB had been flushed. It did so because it needs to walk that array of pages while still holding the page table lock, and our mmu_gather infrastructure allows for batching quite a lot of pages. We may have thousands on pages queued up for freeing, and we wanted to walk only the last batch if we then added a dirty page to the queue. However, when I limited it to one batch, I didn't think of the degenerate case of the special first batch that is embedded on-stack in the mmu_gather structure (called "local") and that only has eight entries. So with the right pattern, that "limit delayed rmap to just one batch" will trigger over and over in that first small batch, and we'll waste a lot of time flushing TLB's every eight pages. And those right patterns are trivially triggered by just having a shared mappings with lots of adjacent dirty pages. Like the 'page_fault3' subtest of the 'will-it-scale' benchmark, that just maps a shared area, dirties all pages, and unmaps it. Rinse and repeat. We still want to limit the batching, but to fix this (easily triggered) degenerate case, just expand the "only one batch" logic to instead be "only one batch that isn't the special first on-stack ('local') batch". That way, when we need to flush the delayed rmaps, we can still limit our walk to just the last batch - and that first small one. Link: https://lkml.kernel.org/r/CAHk-=whkL5aM1fR7kYUmhHQHBcMUc-bDoFP7EwYjTxy64DGtvw@mail.gmail.com Fixes: 5df397dec7c4 ("mm: delay page_remove_rmap() until after the TLB has been flushed") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: kernel test robot <yujie.liu@intel.com> Link: https://lore.kernel.org/oe-lkp/202212051534.852804af-yujie.liu@intel.com Tested-by: Huang, Ying <ying.huang@intel.com> Tested-by: Hugh Dickins <hughd@google.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: "Yin, Fengwei" <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-06 19:15:09 +00:00
tlb_flush_rmap_batch(&tlb->local, vma);
if (tlb->active != &tlb->local)
tlb_flush_rmap_batch(tlb->active, vma);
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
tlb->delayed_rmap = 0;
}
#endif
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
/*
* We might end up freeing a lot of pages. Reschedule on a regular
* basis to avoid soft lockups in configurations without full
* preemption enabled. The magic number of 512 folios seems to work.
*/
#define MAX_NR_FOLIOS_PER_FREE 512
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch)
{
struct encoded_page **pages = batch->encoded_pages;
unsigned int nr, nr_pages;
mm/mmu_gather: limit free batch count and add schedule point in tlb_batch_pages_flush free a large list of pages maybe cause rcu_sched starved on non-preemptible kernels. howerver free_unref_page_list maybe can't cond_resched as it maybe called in interrupt or atomic context, especially can't detect atomic context in CONFIG_PREEMPTION=n. The issue is detected in guest with kvm cpu 200% overcommit, however I didn't see the warning in the host with the same application. I'm sure that the patch is needed for guest kernel, but no sure for host. To reproduce, set up two virtual machines in one host machine, per vm has the same number cpu and half memory of host. the run ltpstress.sh in per vm, then will see rcu stall warning.kernel is preempt disabled, append kernel command 'preempt=none' if enable dynamic preempt . It could detected in loongson machine(32 core, 128G mem) and ProLiant DL380 Gen9(x86 E5-2680, 28 core, 64G mem) tlb flush batch count depends on PAGE_SIZE, it's too large if PAGE_SIZE > 4K, here limit free batch count with 512. And add schedule point in tlb_batch_pages_flush. rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19 [...] Call Trace: free_unref_page_list+0x19c/0x270 release_pages+0x3cc/0x498 tlb_flush_mmu_free+0x44/0x70 zap_pte_range+0x450/0x738 unmap_page_range+0x108/0x240 unmap_vmas+0x74/0xf0 unmap_region+0xb0/0x120 do_munmap+0x264/0x438 vm_munmap+0x58/0xa0 sys_munmap+0x10/0x20 syscall_common+0x24/0x38 Link: https://lkml.kernel.org/r/20220317072857.2635262-1-wangjianxing@loongson.cn Signed-off-by: Jianxing Wang <wangjianxing@loongson.cn> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org> Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-04-29 06:16:12 +00:00
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
while (batch->nr) {
if (!page_poisoning_enabled_static() && !want_init_on_free()) {
nr = min(MAX_NR_FOLIOS_PER_FREE, batch->nr);
mm/mmu_gather: limit free batch count and add schedule point in tlb_batch_pages_flush free a large list of pages maybe cause rcu_sched starved on non-preemptible kernels. howerver free_unref_page_list maybe can't cond_resched as it maybe called in interrupt or atomic context, especially can't detect atomic context in CONFIG_PREEMPTION=n. The issue is detected in guest with kvm cpu 200% overcommit, however I didn't see the warning in the host with the same application. I'm sure that the patch is needed for guest kernel, but no sure for host. To reproduce, set up two virtual machines in one host machine, per vm has the same number cpu and half memory of host. the run ltpstress.sh in per vm, then will see rcu stall warning.kernel is preempt disabled, append kernel command 'preempt=none' if enable dynamic preempt . It could detected in loongson machine(32 core, 128G mem) and ProLiant DL380 Gen9(x86 E5-2680, 28 core, 64G mem) tlb flush batch count depends on PAGE_SIZE, it's too large if PAGE_SIZE > 4K, here limit free batch count with 512. And add schedule point in tlb_batch_pages_flush. rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19 [...] Call Trace: free_unref_page_list+0x19c/0x270 release_pages+0x3cc/0x498 tlb_flush_mmu_free+0x44/0x70 zap_pte_range+0x450/0x738 unmap_page_range+0x108/0x240 unmap_vmas+0x74/0xf0 unmap_region+0xb0/0x120 do_munmap+0x264/0x438 vm_munmap+0x58/0xa0 sys_munmap+0x10/0x20 syscall_common+0x24/0x38 Link: https://lkml.kernel.org/r/20220317072857.2635262-1-wangjianxing@loongson.cn Signed-off-by: Jianxing Wang <wangjianxing@loongson.cn> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org> Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-04-29 06:16:12 +00:00
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
/*
* Make sure we cover page + nr_pages, and don't leave
* nr_pages behind when capping the number of entries.
*/
if (unlikely(encoded_page_flags(pages[nr - 1]) &
ENCODED_PAGE_BIT_NR_PAGES_NEXT))
nr++;
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
} else {
/*
* With page poisoning and init_on_free, the time it
* takes to free memory grows proportionally with the
* actual memory size. Therefore, limit based on the
* actual memory size and not the number of involved
* folios.
*/
for (nr = 0, nr_pages = 0;
nr < batch->nr && nr_pages < MAX_NR_FOLIOS_PER_FREE;
nr++) {
if (unlikely(encoded_page_flags(pages[nr]) &
ENCODED_PAGE_BIT_NR_PAGES_NEXT))
nr_pages += encoded_nr_pages(pages[++nr]);
else
nr_pages++;
}
}
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
free_pages_and_swap_cache(pages, nr);
pages += nr;
batch->nr -= nr;
mm/mmu_gather: limit free batch count and add schedule point in tlb_batch_pages_flush free a large list of pages maybe cause rcu_sched starved on non-preemptible kernels. howerver free_unref_page_list maybe can't cond_resched as it maybe called in interrupt or atomic context, especially can't detect atomic context in CONFIG_PREEMPTION=n. The issue is detected in guest with kvm cpu 200% overcommit, however I didn't see the warning in the host with the same application. I'm sure that the patch is needed for guest kernel, but no sure for host. To reproduce, set up two virtual machines in one host machine, per vm has the same number cpu and half memory of host. the run ltpstress.sh in per vm, then will see rcu stall warning.kernel is preempt disabled, append kernel command 'preempt=none' if enable dynamic preempt . It could detected in loongson machine(32 core, 128G mem) and ProLiant DL380 Gen9(x86 E5-2680, 28 core, 64G mem) tlb flush batch count depends on PAGE_SIZE, it's too large if PAGE_SIZE > 4K, here limit free batch count with 512. And add schedule point in tlb_batch_pages_flush. rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19 [...] Call Trace: free_unref_page_list+0x19c/0x270 release_pages+0x3cc/0x498 tlb_flush_mmu_free+0x44/0x70 zap_pte_range+0x450/0x738 unmap_page_range+0x108/0x240 unmap_vmas+0x74/0xf0 unmap_region+0xb0/0x120 do_munmap+0x264/0x438 vm_munmap+0x58/0xa0 sys_munmap+0x10/0x20 syscall_common+0x24/0x38 Link: https://lkml.kernel.org/r/20220317072857.2635262-1-wangjianxing@loongson.cn Signed-off-by: Jianxing Wang <wangjianxing@loongson.cn> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org> Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-04-29 06:16:12 +00:00
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
cond_resched();
}
mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing In tlb_batch_pages_flush(), we can end up freeing up to 512 pages or now up to 256 folio fragments that span more than one page, before we conditionally reschedule. It's a pain that we have to handle cond_resched() in tlb_batch_pages_flush() manually and cannot simply handle it in release_pages() -- release_pages() can be called from atomic context. Well, in a perfect world we wouldn't have to make our code more complicated at all. With page poisoning and init_on_free, we might now run into soft lockups when we free a lot of rather large folio fragments, because page freeing time then depends on the actual memory size we are freeing instead of on the number of folios that are involved. In the absolute (unlikely) worst case, on arm64 with 64k we will be able to free up to 256 folio fragments that each span 512 MiB: zeroing out 128 GiB does sound like it might take a while. But instead of ignoring this unlikely case, let's just handle it. So, let's teach tlb_batch_pages_flush() that there are some configurations where page freeing is horribly slow, and let's reschedule more frequently -- similarly like we did for now before we had large folio fragments in there. Avoid yet another loop over all encoded pages in the common case by handling that separately. Note that with page poisoning/zeroing, we might now end up freeing only a single folio fragment at a time that might exceed the old 512 pages limit: but if we cannot even free a single MAX_ORDER page on a system without running into soft lockups, something else is already completely bogus. Freeing a PMD-mapped THP would similarly cause trouble. In theory, we might even free 511 order-0 pages + a single MAX_ORDER page, effectively having to zero out 8703 pages on arm64 with 64k, translating to ~544 MiB of memory: however, if 512 MiB doesn't result in soft lockups, 544 MiB is unlikely to result in soft lockups, so we won't care about that for the time being. In the future, we might want to detect if handling cond_resched() is required at all, and just not do any of that with full preemption enabled. Link: https://lkml.kernel.org/r/20240214204435.167852-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:34 +00:00
}
static void tlb_batch_pages_flush(struct mmu_gather *tlb)
{
struct mmu_gather_batch *batch;
for (batch = &tlb->local; batch && batch->nr; batch = batch->next)
__tlb_batch_free_encoded_pages(batch);
tlb->active = &tlb->local;
}
static void tlb_batch_list_free(struct mmu_gather *tlb)
{
struct mmu_gather_batch *batch, *next;
for (batch = tlb->local.next; batch; batch = next) {
next = batch->next;
free_pages((unsigned long)batch, 0);
}
tlb->local.next = NULL;
}
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
static bool __tlb_remove_folio_pages_size(struct mmu_gather *tlb,
struct page *page, unsigned int nr_pages, bool delay_rmap,
int page_size)
{
mm/mmu_gather: define ENCODED_PAGE_FLAG_DELAY_RMAP Nowadays, encoded pages are only used in mmu_gather handling. Let's update the documentation, and define ENCODED_PAGE_BIT_DELAY_RMAP. While at it, rename ENCODE_PAGE_BITS to ENCODED_PAGE_BITS. If encoded page pointers would ever be used in other context again, we'd likely want to change the defines to reflect their context (e.g., ENCODED_PAGE_FLAG_MMU_GATHER_DELAY_RMAP). For now, let's keep it simple. This is a preparation for using the remaining spare bit to indicate that the next item in an array of encoded pages is a "nr_pages" argument and not an encoded page. Link: https://lkml.kernel.org/r/20240214204435.167852-7-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:31 +00:00
int flags = delay_rmap ? ENCODED_PAGE_BIT_DELAY_RMAP : 0;
struct mmu_gather_batch *batch;
VM_BUG_ON(!tlb->end);
#ifdef CONFIG_MMU_GATHER_PAGE_SIZE
VM_WARN_ON(tlb->page_size != page_size);
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
VM_WARN_ON_ONCE(nr_pages != 1 && page_size != PAGE_SIZE);
VM_WARN_ON_ONCE(page_folio(page) != page_folio(page + nr_pages - 1));
#endif
batch = tlb->active;
/*
* Add the page and check if we are full. If so
* force a flush.
*/
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
if (likely(nr_pages == 1)) {
batch->encoded_pages[batch->nr++] = encode_page(page, flags);
} else {
flags |= ENCODED_PAGE_BIT_NR_PAGES_NEXT;
batch->encoded_pages[batch->nr++] = encode_page(page, flags);
batch->encoded_pages[batch->nr++] = encode_nr_pages(nr_pages);
}
/*
* Make sure that we can always add another "page" + "nr_pages",
* requiring two entries instead of only a single one.
*/
if (batch->nr >= batch->max - 1) {
if (!tlb_next_batch(tlb))
return true;
batch = tlb->active;
}
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
VM_BUG_ON_PAGE(batch->nr > batch->max - 1, page);
return false;
}
mm/mmu_gather: add __tlb_remove_folio_pages() Add __tlb_remove_folio_pages(), which will remove multiple consecutive pages that belong to the same large folio, instead of only a single page. We'll be using this function when optimizing unmapping/zapping of large folios that are mapped by PTEs. We're using the remaining spare bit in an encoded_page to indicate that the next enoced page in an array contains actually shifted "nr_pages". Teach swap/freeing code about putting multiple folio references, and delayed rmap handling to remove page ranges of a folio. This extension allows for still gathering almost as many small folios as we used to (-1, because we have to prepare for a possibly bigger next entry), but still allows for gathering consecutive pages that belong to the same large folio. Note that we don't pass the folio pointer, because it is not required for now. Further, we don't support page_size != PAGE_SIZE, it won't be required for simple PTE batching. We have to provide a separate s390 implementation, but it's fairly straight forward. Another, more invasive and likely more expensive, approach would be to use folio+range or a PFN range instead of page+nr_pages. But, we should do that consistently for the whole mmu_gather. For now, let's keep it simple and add "nr_pages" only. Note that it is now possible to gather significantly more pages: In the past, we were able to gather ~10000 pages, now we can also gather ~5000 folio fragments that span multiple pages. A folio fragment on x86-64 can span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192 pages (512 MiB THP). Gathering more memory is not considered something we should worry about, especially because these are already corner cases. While we can gather more total memory, we won't free more folio fragments. As long as page freeing time primarily only depends on the number of involved folios, there is no effective change for !preempt configurations. However, we'll adjust tlb_batch_pages_flush() separately to handle corner cases where page freeing time grows proportionally with the actual memory size. Link: https://lkml.kernel.org/r/20240214204435.167852-9-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Yin Fengwei <fengwei.yin@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-14 20:44:33 +00:00
bool __tlb_remove_folio_pages(struct mmu_gather *tlb, struct page *page,
unsigned int nr_pages, bool delay_rmap)
{
return __tlb_remove_folio_pages_size(tlb, page, nr_pages, delay_rmap,
PAGE_SIZE);
}
bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
bool delay_rmap, int page_size)
{
return __tlb_remove_folio_pages_size(tlb, page, 1, delay_rmap, page_size);
}
#endif /* MMU_GATHER_NO_GATHER */
#ifdef CONFIG_MMU_GATHER_TABLE_FREE
static void __tlb_remove_table_free(struct mmu_table_batch *batch)
{
int i;
for (i = 0; i < batch->nr; i++)
__tlb_remove_table(batch->tables[i]);
free_page((unsigned long)batch);
}
#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
/*
* Semi RCU freeing of the page directories.
*
* This is needed by some architectures to implement software pagetable walkers.
*
* gup_fast() and other software pagetable walkers do a lockless page-table
* walk and therefore needs some synchronization with the freeing of the page
* directories. The chosen means to accomplish that is by disabling IRQs over
* the walk.
*
* Architectures that use IPIs to flush TLBs will then automagically DTRT,
* since we unlink the page, flush TLBs, free the page. Since the disabling of
* IRQs delays the completion of the TLB flush we can never observe an already
* freed page.
*
* Architectures that do not have this (PPC) need to delay the freeing by some
* other means, this is that means.
*
* What we do is batch the freed directory pages (tables) and RCU free them.
* We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
* holds off grace periods.
*
* However, in order to batch these pages we need to allocate storage, this
* allocation is deep inside the MM code and can thus easily fail on memory
* pressure. To guarantee progress we fall back to single table freeing, see
* the implementation of tlb_remove_table_one().
*
*/
static void tlb_remove_table_smp_sync(void *arg)
{
/* Simply deliver the interrupt */
}
void tlb_remove_table_sync_one(void)
{
/*
* This isn't an RCU grace period and hence the page-tables cannot be
* assumed to be actually RCU-freed.
*
* It is however sufficient for software page-table walkers that rely on
* IRQ disabling.
*/
smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
}
static void tlb_remove_table_rcu(struct rcu_head *head)
{
__tlb_remove_table_free(container_of(head, struct mmu_table_batch, rcu));
}
static void tlb_remove_table_free(struct mmu_table_batch *batch)
{
call_rcu(&batch->rcu, tlb_remove_table_rcu);
}
#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
static void tlb_remove_table_free(struct mmu_table_batch *batch)
{
__tlb_remove_table_free(batch);
}
#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
/*
* If we want tlb_remove_table() to imply TLB invalidates.
*/
static inline void tlb_table_invalidate(struct mmu_gather *tlb)
{
if (tlb_needs_table_invalidate()) {
/*
* Invalidate page-table caches used by hardware walkers. Then
* we still need to RCU-sched wait while freeing the pages
* because software walkers can still be in-flight.
*/
tlb_flush_mmu_tlbonly(tlb);
}
}
static void tlb_remove_table_one(void *table)
{
tlb_remove_table_sync_one();
__tlb_remove_table(table);
}
static void tlb_table_flush(struct mmu_gather *tlb)
{
struct mmu_table_batch **batch = &tlb->batch;
if (*batch) {
tlb_table_invalidate(tlb);
tlb_remove_table_free(*batch);
*batch = NULL;
}
}
void tlb_remove_table(struct mmu_gather *tlb, void *table)
{
struct mmu_table_batch **batch = &tlb->batch;
if (*batch == NULL) {
*batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
if (*batch == NULL) {
tlb_table_invalidate(tlb);
tlb_remove_table_one(table);
return;
}
(*batch)->nr = 0;
}
(*batch)->tables[(*batch)->nr++] = table;
if ((*batch)->nr == MAX_TABLE_BATCH)
tlb_table_flush(tlb);
}
static inline void tlb_table_init(struct mmu_gather *tlb)
{
tlb->batch = NULL;
}
#else /* !CONFIG_MMU_GATHER_TABLE_FREE */
static inline void tlb_table_flush(struct mmu_gather *tlb) { }
static inline void tlb_table_init(struct mmu_gather *tlb) { }
#endif /* CONFIG_MMU_GATHER_TABLE_FREE */
static void tlb_flush_mmu_free(struct mmu_gather *tlb)
{
tlb_table_flush(tlb);
#ifndef CONFIG_MMU_GATHER_NO_GATHER
tlb_batch_pages_flush(tlb);
#endif
}
void tlb_flush_mmu(struct mmu_gather *tlb)
{
tlb_flush_mmu_tlbonly(tlb);
tlb_flush_mmu_free(tlb);
}
static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
bool fullmm)
{
tlb->mm = mm;
tlb->fullmm = fullmm;
#ifndef CONFIG_MMU_GATHER_NO_GATHER
tlb->need_flush_all = 0;
tlb->local.next = NULL;
tlb->local.nr = 0;
tlb->local.max = ARRAY_SIZE(tlb->__pages);
tlb->active = &tlb->local;
tlb->batch_count = 0;
#endif
mm: delay page_remove_rmap() until after the TLB has been flushed When we remove a page table entry, we are very careful to only free the page after we have flushed the TLB, because other CPUs could still be using the page through stale TLB entries until after the flush. However, we have removed the rmap entry for that page early, which means that functions like folio_mkclean() would end up not serializing with the page table lock because the page had already been made invisible to rmap. And that is a problem, because while the TLB entry exists, we could end up with the following situation: (a) one CPU could come in and clean it, never seeing our mapping of the page (b) another CPU could continue to use the stale and dirty TLB entry and continue to write to said page resulting in a page that has been dirtied, but then marked clean again, all while another CPU might have dirtied it some more. End result: possibly lost dirty data. This extends our current TLB gather infrastructure to optionally track a "should I do a delayed page_remove_rmap() for this page after flushing the TLB". It uses the newly introduced 'encoded page pointer' to do that without having to keep separate data around. Note, this is complicated by a couple of issues: - we want to delay the rmap removal, but not past the page table lock, because that simplifies the memcg accounting - only SMP configurations want to delay TLB flushing, since on UP there are obviously no remote TLBs to worry about, and the page table lock means there are no preemption issues either - s390 has its own mmu_gather model that doesn't delay TLB flushing, and as a result also does not want the delayed rmap. As such, we can treat S390 like the UP case and use a common fallback for the "no delays" case. - we can track an enormous number of pages in our mmu_gather structure, with MAX_GATHER_BATCH_COUNT batches of MAX_TABLE_BATCH pages each, all set up to be approximately 10k pending pages. We do not want to have a huge number of batched pages that we then need to check for delayed rmap handling inside the page table lock. Particularly that last point results in a noteworthy detail, where the normal page batch gathering is limited once we have delayed rmaps pending, in such a way that only the last batch (the so-called "active batch") in the mmu_gather structure can have any delayed entries. NOTE! While the "possibly lost dirty data" sounds catastrophic, for this all to happen you need to have a user thread doing either madvise() with MADV_DONTNEED or a full re-mmap() of the area concurrently with another thread continuing to use said mapping. So arguably this is about user space doing crazy things, but from a VM consistency standpoint it's better if we track the dirty bit properly even when user space goes off the rails. [akpm@linux-foundation.org: fix UP build, per Linus] Link: https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com/ Link: https://lkml.kernel.org/r/20221109203051.1835763-4-torvalds@linux-foundation.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Hugh Dickins <hughd@google.com> Reported-by: Nadav Amit <nadav.amit@gmail.com> Tested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-09 20:30:51 +00:00
tlb->delayed_rmap = 0;
tlb_table_init(tlb);
#ifdef CONFIG_MMU_GATHER_PAGE_SIZE
tlb->page_size = 0;
#endif
__tlb_reset_range(tlb);
inc_tlb_flush_pending(tlb->mm);
}
/**
* tlb_gather_mmu - initialize an mmu_gather structure for page-table tear-down
* @tlb: the mmu_gather structure to initialize
* @mm: the mm_struct of the target address space
*
* Called to initialize an (on-stack) mmu_gather structure for page-table
* tear-down from @mm.
*/
void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm)
{
__tlb_gather_mmu(tlb, mm, false);
}
/**
* tlb_gather_mmu_fullmm - initialize an mmu_gather structure for page-table tear-down
* @tlb: the mmu_gather structure to initialize
* @mm: the mm_struct of the target address space
*
* In this case, @mm is without users and we're going to destroy the
* full address space (exit/execve).
*
* Called to initialize an (on-stack) mmu_gather structure for page-table
* tear-down from @mm.
*/
void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm)
{
__tlb_gather_mmu(tlb, mm, true);
}
/**
* tlb_finish_mmu - finish an mmu_gather structure
* @tlb: the mmu_gather structure to finish
*
* Called at the end of the shootdown operation to free up any resources that
* were required.
*/
void tlb_finish_mmu(struct mmu_gather *tlb)
{
/*
* If there are parallel threads are doing PTE changes on same range
* under non-exclusive lock (e.g., mmap_lock read-side) but defer TLB
mm: mmu_gather: remove __tlb_reset_range() for force flush A few new fields were added to mmu_gather to make TLB flush smarter for huge page by telling what level of page table is changed. __tlb_reset_range() is used to reset all these page table state to unchanged, which is called by TLB flush for parallel mapping changes for the same range under non-exclusive lock (i.e. read mmap_sem). Before commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap"), the syscalls (e.g. MADV_DONTNEED, MADV_FREE) which may update PTEs in parallel don't remove page tables. But, the forementioned commit may do munmap() under read mmap_sem and free page tables. This may result in program hang on aarch64 reported by Jan Stancek. The problem could be reproduced by his test program with slightly modified below. ---8<--- static int map_size = 4096; static int num_iter = 500; static long threads_total; static void *distant_area; void *map_write_unmap(void *ptr) { int *fd = ptr; unsigned char *map_address; int i, j = 0; for (i = 0; i < num_iter; i++) { map_address = mmap(distant_area, (size_t) map_size, PROT_WRITE | PROT_READ, MAP_SHARED | MAP_ANONYMOUS, -1, 0); if (map_address == MAP_FAILED) { perror("mmap"); exit(1); } for (j = 0; j < map_size; j++) map_address[j] = 'b'; if (munmap(map_address, map_size) == -1) { perror("munmap"); exit(1); } } return NULL; } void *dummy(void *ptr) { return NULL; } int main(void) { pthread_t thid[2]; /* hint for mmap in map_write_unmap() */ distant_area = mmap(0, DISTANT_MMAP_SIZE, PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); munmap(distant_area, (size_t)DISTANT_MMAP_SIZE); distant_area += DISTANT_MMAP_SIZE / 2; while (1) { pthread_create(&thid[0], NULL, map_write_unmap, NULL); pthread_create(&thid[1], NULL, dummy, NULL); pthread_join(thid[0], NULL); pthread_join(thid[1], NULL); } } ---8<--- The program may bring in parallel execution like below: t1 t2 munmap(map_address) downgrade_write(&mm->mmap_sem); unmap_region() tlb_gather_mmu() inc_tlb_flush_pending(tlb->mm); free_pgtables() tlb->freed_tables = 1 tlb->cleared_pmds = 1 pthread_exit() madvise(thread_stack, 8M, MADV_DONTNEED) zap_page_range() tlb_gather_mmu() inc_tlb_flush_pending(tlb->mm); tlb_finish_mmu() if (mm_tlb_flush_nested(tlb->mm)) __tlb_reset_range() __tlb_reset_range() would reset freed_tables and cleared_* bits, but this may cause inconsistency for munmap() which do free page tables. Then it may result in some architectures, e.g. aarch64, may not flush TLB completely as expected to have stale TLB entries remained. Use fullmm flush since it yields much better performance on aarch64 and non-fullmm doesn't yields significant difference on x86. The original proposed fix came from Jan Stancek who mainly debugged this issue, I just wrapped up everything together. Jan's testing results: v5.2-rc2-24-gbec7550cca10 -------------------------- mean stddev real 37.382 2.780 user 1.420 0.078 sys 54.658 1.855 v5.2-rc2-24-gbec7550cca10 + "mm: mmu_gather: remove __tlb_reset_range() for force flush" ---------------------------------------------------------------------------------------_ mean stddev real 37.119 2.105 user 1.548 0.087 sys 55.698 1.357 [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1558322252-113575-1-git-send-email-yang.shi@linux.alibaba.com Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Signed-off-by: Jan Stancek <jstancek@redhat.com> Reported-by: Jan Stancek <jstancek@redhat.com> Tested-by: Jan Stancek <jstancek@redhat.com> Suggested-by: Will Deacon <will.deacon@arm.com> Tested-by: Will Deacon <will.deacon@arm.com> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Nick Piggin <npiggin@gmail.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: <stable@vger.kernel.org> [4.20+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-06-13 22:56:05 +00:00
* flush by batching, one thread may end up seeing inconsistent PTEs
* and result in having stale TLB entries. So flush TLB forcefully
* if we detect parallel PTE batching threads.
*
* However, some syscalls, e.g. munmap(), may free page tables, this
* needs force flush everything in the given range. Otherwise this
* may result in having stale TLB entries for some architectures,
* e.g. aarch64, that could specify flush what level TLB.
*/
if (mm_tlb_flush_nested(tlb->mm)) {
mm: mmu_gather: remove __tlb_reset_range() for force flush A few new fields were added to mmu_gather to make TLB flush smarter for huge page by telling what level of page table is changed. __tlb_reset_range() is used to reset all these page table state to unchanged, which is called by TLB flush for parallel mapping changes for the same range under non-exclusive lock (i.e. read mmap_sem). Before commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap"), the syscalls (e.g. MADV_DONTNEED, MADV_FREE) which may update PTEs in parallel don't remove page tables. But, the forementioned commit may do munmap() under read mmap_sem and free page tables. This may result in program hang on aarch64 reported by Jan Stancek. The problem could be reproduced by his test program with slightly modified below. ---8<--- static int map_size = 4096; static int num_iter = 500; static long threads_total; static void *distant_area; void *map_write_unmap(void *ptr) { int *fd = ptr; unsigned char *map_address; int i, j = 0; for (i = 0; i < num_iter; i++) { map_address = mmap(distant_area, (size_t) map_size, PROT_WRITE | PROT_READ, MAP_SHARED | MAP_ANONYMOUS, -1, 0); if (map_address == MAP_FAILED) { perror("mmap"); exit(1); } for (j = 0; j < map_size; j++) map_address[j] = 'b'; if (munmap(map_address, map_size) == -1) { perror("munmap"); exit(1); } } return NULL; } void *dummy(void *ptr) { return NULL; } int main(void) { pthread_t thid[2]; /* hint for mmap in map_write_unmap() */ distant_area = mmap(0, DISTANT_MMAP_SIZE, PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); munmap(distant_area, (size_t)DISTANT_MMAP_SIZE); distant_area += DISTANT_MMAP_SIZE / 2; while (1) { pthread_create(&thid[0], NULL, map_write_unmap, NULL); pthread_create(&thid[1], NULL, dummy, NULL); pthread_join(thid[0], NULL); pthread_join(thid[1], NULL); } } ---8<--- The program may bring in parallel execution like below: t1 t2 munmap(map_address) downgrade_write(&mm->mmap_sem); unmap_region() tlb_gather_mmu() inc_tlb_flush_pending(tlb->mm); free_pgtables() tlb->freed_tables = 1 tlb->cleared_pmds = 1 pthread_exit() madvise(thread_stack, 8M, MADV_DONTNEED) zap_page_range() tlb_gather_mmu() inc_tlb_flush_pending(tlb->mm); tlb_finish_mmu() if (mm_tlb_flush_nested(tlb->mm)) __tlb_reset_range() __tlb_reset_range() would reset freed_tables and cleared_* bits, but this may cause inconsistency for munmap() which do free page tables. Then it may result in some architectures, e.g. aarch64, may not flush TLB completely as expected to have stale TLB entries remained. Use fullmm flush since it yields much better performance on aarch64 and non-fullmm doesn't yields significant difference on x86. The original proposed fix came from Jan Stancek who mainly debugged this issue, I just wrapped up everything together. Jan's testing results: v5.2-rc2-24-gbec7550cca10 -------------------------- mean stddev real 37.382 2.780 user 1.420 0.078 sys 54.658 1.855 v5.2-rc2-24-gbec7550cca10 + "mm: mmu_gather: remove __tlb_reset_range() for force flush" ---------------------------------------------------------------------------------------_ mean stddev real 37.119 2.105 user 1.548 0.087 sys 55.698 1.357 [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1558322252-113575-1-git-send-email-yang.shi@linux.alibaba.com Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Signed-off-by: Jan Stancek <jstancek@redhat.com> Reported-by: Jan Stancek <jstancek@redhat.com> Tested-by: Jan Stancek <jstancek@redhat.com> Suggested-by: Will Deacon <will.deacon@arm.com> Tested-by: Will Deacon <will.deacon@arm.com> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Nick Piggin <npiggin@gmail.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: <stable@vger.kernel.org> [4.20+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-06-13 22:56:05 +00:00
/*
* The aarch64 yields better performance with fullmm by
* avoiding multiple CPUs spamming TLBI messages at the
* same time.
*
* On x86 non-fullmm doesn't yield significant difference
* against fullmm.
*/
tlb->fullmm = 1;
__tlb_reset_range(tlb);
mm: mmu_gather: remove __tlb_reset_range() for force flush A few new fields were added to mmu_gather to make TLB flush smarter for huge page by telling what level of page table is changed. __tlb_reset_range() is used to reset all these page table state to unchanged, which is called by TLB flush for parallel mapping changes for the same range under non-exclusive lock (i.e. read mmap_sem). Before commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap"), the syscalls (e.g. MADV_DONTNEED, MADV_FREE) which may update PTEs in parallel don't remove page tables. But, the forementioned commit may do munmap() under read mmap_sem and free page tables. This may result in program hang on aarch64 reported by Jan Stancek. The problem could be reproduced by his test program with slightly modified below. ---8<--- static int map_size = 4096; static int num_iter = 500; static long threads_total; static void *distant_area; void *map_write_unmap(void *ptr) { int *fd = ptr; unsigned char *map_address; int i, j = 0; for (i = 0; i < num_iter; i++) { map_address = mmap(distant_area, (size_t) map_size, PROT_WRITE | PROT_READ, MAP_SHARED | MAP_ANONYMOUS, -1, 0); if (map_address == MAP_FAILED) { perror("mmap"); exit(1); } for (j = 0; j < map_size; j++) map_address[j] = 'b'; if (munmap(map_address, map_size) == -1) { perror("munmap"); exit(1); } } return NULL; } void *dummy(void *ptr) { return NULL; } int main(void) { pthread_t thid[2]; /* hint for mmap in map_write_unmap() */ distant_area = mmap(0, DISTANT_MMAP_SIZE, PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); munmap(distant_area, (size_t)DISTANT_MMAP_SIZE); distant_area += DISTANT_MMAP_SIZE / 2; while (1) { pthread_create(&thid[0], NULL, map_write_unmap, NULL); pthread_create(&thid[1], NULL, dummy, NULL); pthread_join(thid[0], NULL); pthread_join(thid[1], NULL); } } ---8<--- The program may bring in parallel execution like below: t1 t2 munmap(map_address) downgrade_write(&mm->mmap_sem); unmap_region() tlb_gather_mmu() inc_tlb_flush_pending(tlb->mm); free_pgtables() tlb->freed_tables = 1 tlb->cleared_pmds = 1 pthread_exit() madvise(thread_stack, 8M, MADV_DONTNEED) zap_page_range() tlb_gather_mmu() inc_tlb_flush_pending(tlb->mm); tlb_finish_mmu() if (mm_tlb_flush_nested(tlb->mm)) __tlb_reset_range() __tlb_reset_range() would reset freed_tables and cleared_* bits, but this may cause inconsistency for munmap() which do free page tables. Then it may result in some architectures, e.g. aarch64, may not flush TLB completely as expected to have stale TLB entries remained. Use fullmm flush since it yields much better performance on aarch64 and non-fullmm doesn't yields significant difference on x86. The original proposed fix came from Jan Stancek who mainly debugged this issue, I just wrapped up everything together. Jan's testing results: v5.2-rc2-24-gbec7550cca10 -------------------------- mean stddev real 37.382 2.780 user 1.420 0.078 sys 54.658 1.855 v5.2-rc2-24-gbec7550cca10 + "mm: mmu_gather: remove __tlb_reset_range() for force flush" ---------------------------------------------------------------------------------------_ mean stddev real 37.119 2.105 user 1.548 0.087 sys 55.698 1.357 [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1558322252-113575-1-git-send-email-yang.shi@linux.alibaba.com Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Signed-off-by: Jan Stancek <jstancek@redhat.com> Reported-by: Jan Stancek <jstancek@redhat.com> Tested-by: Jan Stancek <jstancek@redhat.com> Suggested-by: Will Deacon <will.deacon@arm.com> Tested-by: Will Deacon <will.deacon@arm.com> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Nick Piggin <npiggin@gmail.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: <stable@vger.kernel.org> [4.20+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-06-13 22:56:05 +00:00
tlb->freed_tables = 1;
}
tlb_flush_mmu(tlb);
#ifndef CONFIG_MMU_GATHER_NO_GATHER
tlb_batch_list_free(tlb);
#endif
dec_tlb_flush_pending(tlb->mm);
}