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mm: add pte_batch_hint() to reduce scanning in folio_pte_batch()

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Some architectures (e.g.  arm64) can tell from looking at a pte, if some
follow-on ptes also map contiguous physical memory with the same pgprot. 
(for arm64, these are contpte mappings).

Take advantage of this knowledge to optimize folio_pte_batch() so that it
can skip these ptes when scanning to create a batch.  By default, if an
arch does not opt-in, folio_pte_batch() returns a compile-time 1, so the
changes are optimized out and the behaviour is as before.

arm64 will opt-in to providing this hint in the next patch, which will
greatly reduce the cost of ptep_get() when scanning a range of contptes.

Link: https://lkml.kernel.org/r/20240215103205.2607016-16-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Tested-by: John Hubbard <jhubbard@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ryan Roberts 2024-02-15 10:32:02 +00:00 committed by Andrew Morton
parent 6b1e4efb6f
commit c6ec76a2eb
2 changed files with 33 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
include/linux/pgtable.h
View File

@ -212,6 +212,27 @@ static inline int pmd_dirty(pmd_t pmd)
#define arch_flush_lazy_mmu_mode() do {} while (0)
#endif
#ifndef pte_batch_hint
/**
* pte_batch_hint - Number of pages that can be added to batch without scanning.
* @ptep: Page table pointer for the entry.
* @pte: Page table entry.
*
* Some architectures know that a set of contiguous ptes all map the same
* contiguous memory with the same permissions. In this case, it can provide a
* hint to aid pte batching without the core code needing to scan every pte.
*
* An architecture implementation may ignore the PTE accessed state. Further,
* the dirty state must apply atomically to all the PTEs described by the hint.
*
* May be overridden by the architecture, else pte_batch_hint is always 1.
*/
static inline unsigned int pte_batch_hint(pte_t *ptep, pte_t pte)
{
return 1;
}
#endif
#ifndef pte_advance_pfn
static inline pte_t pte_advance_pfn(pte_t pte, unsigned long nr)
{

19
mm/memory.c
View File

@ -988,16 +988,20 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
{
unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio);
const pte_t *end_ptep = start_ptep + max_nr;
pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte), flags);
pte_t *ptep = start_ptep + 1;
pte_t expected_pte, *ptep;
bool writable;
int nr;
if (any_writable)
*any_writable = false;
VM_WARN_ON_FOLIO(!pte_present(pte), folio);
while (ptep != end_ptep) {
nr = pte_batch_hint(start_ptep, pte);
expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags);
ptep = start_ptep + nr;
while (ptep < end_ptep) {
pte = ptep_get(ptep);
if (any_writable)
writable = !!pte_write(pte);
@ -1011,17 +1015,18 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
* corner cases the next PFN might fall into a different
* folio.
*/
if (pte_pfn(pte) == folio_end_pfn)
if (pte_pfn(pte) >= folio_end_pfn)
break;
if (any_writable)
*any_writable |= writable;
expected_pte = pte_next_pfn(expected_pte);
ptep++;
nr = pte_batch_hint(ptep, pte);
expected_pte = pte_advance_pfn(expected_pte, nr);
ptep += nr;
}
return ptep - start_ptep;
return min(ptep - start_ptep, max_nr);
}
/*