linux/mm/ksm.c
Hugh Dickins b402826033 ksm: rename kernel_pages_allocated
We're not implementing swapping of KSM pages in its first release;
but when that follows, "kernel_pages_allocated" will be a very poor
name for the sysfs file showing number of nodes in the stable tree:
rename that to "pages_shared" throughout.

But we already have a "pages_shared", counting those page slots
sharing the shared pages: first rename that to... "pages_sharing".

What will become of "max_kernel_pages" when the pages shared can
be swapped?  I guess it will just be removed, so keep that name.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 07:17:32 -07:00

1536 lines
40 KiB
C

/*
* Memory merging support.
*
* This code enables dynamic sharing of identical pages found in different
* memory areas, even if they are not shared by fork()
*
* Copyright (C) 2008-2009 Red Hat, Inc.
* Authors:
* Izik Eidus
* Andrea Arcangeli
* Chris Wright
* Hugh Dickins
*
* This work is licensed under the terms of the GNU GPL, version 2.
*/
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/mman.h>
#include <linux/sched.h>
#include <linux/rwsem.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/spinlock.h>
#include <linux/jhash.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
#include <linux/mmu_notifier.h>
#include <linux/ksm.h>
#include <asm/tlbflush.h>
/*
* A few notes about the KSM scanning process,
* to make it easier to understand the data structures below:
*
* In order to reduce excessive scanning, KSM sorts the memory pages by their
* contents into a data structure that holds pointers to the pages' locations.
*
* Since the contents of the pages may change at any moment, KSM cannot just
* insert the pages into a normal sorted tree and expect it to find anything.
* Therefore KSM uses two data structures - the stable and the unstable tree.
*
* The stable tree holds pointers to all the merged pages (ksm pages), sorted
* by their contents. Because each such page is write-protected, searching on
* this tree is fully assured to be working (except when pages are unmapped),
* and therefore this tree is called the stable tree.
*
* In addition to the stable tree, KSM uses a second data structure called the
* unstable tree: this tree holds pointers to pages which have been found to
* be "unchanged for a period of time". The unstable tree sorts these pages
* by their contents, but since they are not write-protected, KSM cannot rely
* upon the unstable tree to work correctly - the unstable tree is liable to
* be corrupted as its contents are modified, and so it is called unstable.
*
* KSM solves this problem by several techniques:
*
* 1) The unstable tree is flushed every time KSM completes scanning all
* memory areas, and then the tree is rebuilt again from the beginning.
* 2) KSM will only insert into the unstable tree, pages whose hash value
* has not changed since the previous scan of all memory areas.
* 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
* colors of the nodes and not on their contents, assuring that even when
* the tree gets "corrupted" it won't get out of balance, so scanning time
* remains the same (also, searching and inserting nodes in an rbtree uses
* the same algorithm, so we have no overhead when we flush and rebuild).
* 4) KSM never flushes the stable tree, which means that even if it were to
* take 10 attempts to find a page in the unstable tree, once it is found,
* it is secured in the stable tree. (When we scan a new page, we first
* compare it against the stable tree, and then against the unstable tree.)
*/
/**
* struct mm_slot - ksm information per mm that is being scanned
* @link: link to the mm_slots hash list
* @mm_list: link into the mm_slots list, rooted in ksm_mm_head
* @rmap_list: head for this mm_slot's list of rmap_items
* @mm: the mm that this information is valid for
*/
struct mm_slot {
struct hlist_node link;
struct list_head mm_list;
struct list_head rmap_list;
struct mm_struct *mm;
};
/**
* struct ksm_scan - cursor for scanning
* @mm_slot: the current mm_slot we are scanning
* @address: the next address inside that to be scanned
* @rmap_item: the current rmap that we are scanning inside the rmap_list
* @seqnr: count of completed full scans (needed when removing unstable node)
*
* There is only the one ksm_scan instance of this cursor structure.
*/
struct ksm_scan {
struct mm_slot *mm_slot;
unsigned long address;
struct rmap_item *rmap_item;
unsigned long seqnr;
};
/**
* struct rmap_item - reverse mapping item for virtual addresses
* @link: link into mm_slot's rmap_list (rmap_list is per mm)
* @mm: the memory structure this rmap_item is pointing into
* @address: the virtual address this rmap_item tracks (+ flags in low bits)
* @oldchecksum: previous checksum of the page at that virtual address
* @node: rb_node of this rmap_item in either unstable or stable tree
* @next: next rmap_item hanging off the same node of the stable tree
* @prev: previous rmap_item hanging off the same node of the stable tree
*/
struct rmap_item {
struct list_head link;
struct mm_struct *mm;
unsigned long address; /* + low bits used for flags below */
union {
unsigned int oldchecksum; /* when unstable */
struct rmap_item *next; /* when stable */
};
union {
struct rb_node node; /* when tree node */
struct rmap_item *prev; /* in stable list */
};
};
#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
#define NODE_FLAG 0x100 /* is a node of unstable or stable tree */
#define STABLE_FLAG 0x200 /* is a node or list item of stable tree */
/* The stable and unstable tree heads */
static struct rb_root root_stable_tree = RB_ROOT;
static struct rb_root root_unstable_tree = RB_ROOT;
#define MM_SLOTS_HASH_HEADS 1024
static struct hlist_head *mm_slots_hash;
static struct mm_slot ksm_mm_head = {
.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
};
static struct ksm_scan ksm_scan = {
.mm_slot = &ksm_mm_head,
};
static struct kmem_cache *rmap_item_cache;
static struct kmem_cache *mm_slot_cache;
/* The number of nodes in the stable tree */
static unsigned long ksm_pages_shared;
/* The number of page slots sharing those nodes */
static unsigned long ksm_pages_sharing;
/* Limit on the number of unswappable pages used */
static unsigned long ksm_max_kernel_pages;
/* Number of pages ksmd should scan in one batch */
static unsigned int ksm_thread_pages_to_scan;
/* Milliseconds ksmd should sleep between batches */
static unsigned int ksm_thread_sleep_millisecs;
#define KSM_RUN_STOP 0
#define KSM_RUN_MERGE 1
#define KSM_RUN_UNMERGE 2
static unsigned int ksm_run;
static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
static DEFINE_MUTEX(ksm_thread_mutex);
static DEFINE_SPINLOCK(ksm_mmlist_lock);
#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
sizeof(struct __struct), __alignof__(struct __struct),\
(__flags), NULL)
static int __init ksm_slab_init(void)
{
rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
if (!rmap_item_cache)
goto out;
mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
if (!mm_slot_cache)
goto out_free;
return 0;
out_free:
kmem_cache_destroy(rmap_item_cache);
out:
return -ENOMEM;
}
static void __init ksm_slab_free(void)
{
kmem_cache_destroy(mm_slot_cache);
kmem_cache_destroy(rmap_item_cache);
mm_slot_cache = NULL;
}
static inline struct rmap_item *alloc_rmap_item(void)
{
return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
}
static inline void free_rmap_item(struct rmap_item *rmap_item)
{
rmap_item->mm = NULL; /* debug safety */
kmem_cache_free(rmap_item_cache, rmap_item);
}
static inline struct mm_slot *alloc_mm_slot(void)
{
if (!mm_slot_cache) /* initialization failed */
return NULL;
return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
}
static inline void free_mm_slot(struct mm_slot *mm_slot)
{
kmem_cache_free(mm_slot_cache, mm_slot);
}
static int __init mm_slots_hash_init(void)
{
mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
GFP_KERNEL);
if (!mm_slots_hash)
return -ENOMEM;
return 0;
}
static void __init mm_slots_hash_free(void)
{
kfree(mm_slots_hash);
}
static struct mm_slot *get_mm_slot(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
struct hlist_head *bucket;
struct hlist_node *node;
bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
% MM_SLOTS_HASH_HEADS];
hlist_for_each_entry(mm_slot, node, bucket, link) {
if (mm == mm_slot->mm)
return mm_slot;
}
return NULL;
}
static void insert_to_mm_slots_hash(struct mm_struct *mm,
struct mm_slot *mm_slot)
{
struct hlist_head *bucket;
bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
% MM_SLOTS_HASH_HEADS];
mm_slot->mm = mm;
INIT_LIST_HEAD(&mm_slot->rmap_list);
hlist_add_head(&mm_slot->link, bucket);
}
static inline int in_stable_tree(struct rmap_item *rmap_item)
{
return rmap_item->address & STABLE_FLAG;
}
/*
* We use break_ksm to break COW on a ksm page: it's a stripped down
*
* if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
* put_page(page);
*
* but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
* in case the application has unmapped and remapped mm,addr meanwhile.
* Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
* mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
*/
static void break_ksm(struct vm_area_struct *vma, unsigned long addr)
{
struct page *page;
int ret;
do {
cond_resched();
page = follow_page(vma, addr, FOLL_GET);
if (!page)
break;
if (PageKsm(page))
ret = handle_mm_fault(vma->vm_mm, vma, addr,
FAULT_FLAG_WRITE);
else
ret = VM_FAULT_WRITE;
put_page(page);
} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS)));
/* Which leaves us looping there if VM_FAULT_OOM: hmmm... */
}
static void __break_cow(struct mm_struct *mm, unsigned long addr)
{
struct vm_area_struct *vma;
vma = find_vma(mm, addr);
if (!vma || vma->vm_start > addr)
return;
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
return;
break_ksm(vma, addr);
}
static void break_cow(struct mm_struct *mm, unsigned long addr)
{
down_read(&mm->mmap_sem);
__break_cow(mm, addr);
up_read(&mm->mmap_sem);
}
static struct page *get_mergeable_page(struct rmap_item *rmap_item)
{
struct mm_struct *mm = rmap_item->mm;
unsigned long addr = rmap_item->address;
struct vm_area_struct *vma;
struct page *page;
down_read(&mm->mmap_sem);
vma = find_vma(mm, addr);
if (!vma || vma->vm_start > addr)
goto out;
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
goto out;
page = follow_page(vma, addr, FOLL_GET);
if (!page)
goto out;
if (PageAnon(page)) {
flush_anon_page(vma, page, addr);
flush_dcache_page(page);
} else {
put_page(page);
out: page = NULL;
}
up_read(&mm->mmap_sem);
return page;
}
/*
* get_ksm_page: checks if the page at the virtual address in rmap_item
* is still PageKsm, in which case we can trust the content of the page,
* and it returns the gotten page; but NULL if the page has been zapped.
*/
static struct page *get_ksm_page(struct rmap_item *rmap_item)
{
struct page *page;
page = get_mergeable_page(rmap_item);
if (page && !PageKsm(page)) {
put_page(page);
page = NULL;
}
return page;
}
/*
* Removing rmap_item from stable or unstable tree.
* This function will clean the information from the stable/unstable tree.
*/
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
{
if (in_stable_tree(rmap_item)) {
struct rmap_item *next_item = rmap_item->next;
if (rmap_item->address & NODE_FLAG) {
if (next_item) {
rb_replace_node(&rmap_item->node,
&next_item->node,
&root_stable_tree);
next_item->address |= NODE_FLAG;
} else {
rb_erase(&rmap_item->node, &root_stable_tree);
ksm_pages_shared--;
}
} else {
struct rmap_item *prev_item = rmap_item->prev;
BUG_ON(prev_item->next != rmap_item);
prev_item->next = next_item;
if (next_item) {
BUG_ON(next_item->prev != rmap_item);
next_item->prev = rmap_item->prev;
}
}
rmap_item->next = NULL;
ksm_pages_sharing--;
} else if (rmap_item->address & NODE_FLAG) {
unsigned char age;
/*
* ksm_thread can and must skip the rb_erase, because
* root_unstable_tree was already reset to RB_ROOT.
* But __ksm_exit has to be careful: do the rb_erase
* if it's interrupting a scan, and this rmap_item was
* inserted by this scan rather than left from before.
*
* Because of the case in which remove_mm_from_lists
* increments seqnr before removing rmaps, unstable_nr
* may even be 2 behind seqnr, but should never be
* further behind. Yes, I did have trouble with this!
*/
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
BUG_ON(age > 2);
if (!age)
rb_erase(&rmap_item->node, &root_unstable_tree);
}
rmap_item->address &= PAGE_MASK;
cond_resched(); /* we're called from many long loops */
}
static void remove_all_slot_rmap_items(struct mm_slot *mm_slot)
{
struct rmap_item *rmap_item, *node;
list_for_each_entry_safe(rmap_item, node, &mm_slot->rmap_list, link) {
remove_rmap_item_from_tree(rmap_item);
list_del(&rmap_item->link);
free_rmap_item(rmap_item);
}
}
static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
struct list_head *cur)
{
struct rmap_item *rmap_item;
while (cur != &mm_slot->rmap_list) {
rmap_item = list_entry(cur, struct rmap_item, link);
cur = cur->next;
remove_rmap_item_from_tree(rmap_item);
list_del(&rmap_item->link);
free_rmap_item(rmap_item);
}
}
/*
* Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
* than check every pte of a given vma, the locking doesn't quite work for
* that - an rmap_item is assigned to the stable tree after inserting ksm
* page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
* rmap_items from parent to child at fork time (so as not to waste time
* if exit comes before the next scan reaches it).
*/
static void unmerge_ksm_pages(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
unsigned long addr;
for (addr = start; addr < end; addr += PAGE_SIZE)
break_ksm(vma, addr);
}
static void unmerge_and_remove_all_rmap_items(void)
{
struct mm_slot *mm_slot;
struct mm_struct *mm;
struct vm_area_struct *vma;
list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) {
mm = mm_slot->mm;
down_read(&mm->mmap_sem);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
continue;
unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
}
remove_all_slot_rmap_items(mm_slot);
up_read(&mm->mmap_sem);
}
spin_lock(&ksm_mmlist_lock);
if (ksm_scan.mm_slot != &ksm_mm_head) {
ksm_scan.mm_slot = &ksm_mm_head;
ksm_scan.seqnr++;
}
spin_unlock(&ksm_mmlist_lock);
}
static void remove_mm_from_lists(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
spin_lock(&ksm_mmlist_lock);
mm_slot = get_mm_slot(mm);
/*
* This mm_slot is always at the scanning cursor when we're
* called from scan_get_next_rmap_item; but it's a special
* case when we're called from __ksm_exit.
*/
if (ksm_scan.mm_slot == mm_slot) {
ksm_scan.mm_slot = list_entry(
mm_slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.address = 0;
ksm_scan.rmap_item = list_entry(
&ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
if (ksm_scan.mm_slot == &ksm_mm_head)
ksm_scan.seqnr++;
}
hlist_del(&mm_slot->link);
list_del(&mm_slot->mm_list);
spin_unlock(&ksm_mmlist_lock);
remove_all_slot_rmap_items(mm_slot);
free_mm_slot(mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
}
static u32 calc_checksum(struct page *page)
{
u32 checksum;
void *addr = kmap_atomic(page, KM_USER0);
checksum = jhash2(addr, PAGE_SIZE / 4, 17);
kunmap_atomic(addr, KM_USER0);
return checksum;
}
static int memcmp_pages(struct page *page1, struct page *page2)
{
char *addr1, *addr2;
int ret;
addr1 = kmap_atomic(page1, KM_USER0);
addr2 = kmap_atomic(page2, KM_USER1);
ret = memcmp(addr1, addr2, PAGE_SIZE);
kunmap_atomic(addr2, KM_USER1);
kunmap_atomic(addr1, KM_USER0);
return ret;
}
static inline int pages_identical(struct page *page1, struct page *page2)
{
return !memcmp_pages(page1, page2);
}
static int write_protect_page(struct vm_area_struct *vma, struct page *page,
pte_t *orig_pte)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long addr;
pte_t *ptep;
spinlock_t *ptl;
int swapped;
int err = -EFAULT;
addr = page_address_in_vma(page, vma);
if (addr == -EFAULT)
goto out;
ptep = page_check_address(page, mm, addr, &ptl, 0);
if (!ptep)
goto out;
if (pte_write(*ptep)) {
pte_t entry;
swapped = PageSwapCache(page);
flush_cache_page(vma, addr, page_to_pfn(page));
/*
* Ok this is tricky, when get_user_pages_fast() run it doesnt
* take any lock, therefore the check that we are going to make
* with the pagecount against the mapcount is racey and
* O_DIRECT can happen right after the check.
* So we clear the pte and flush the tlb before the check
* this assure us that no O_DIRECT can happen after the check
* or in the middle of the check.
*/
entry = ptep_clear_flush(vma, addr, ptep);
/*
* Check that no O_DIRECT or similar I/O is in progress on the
* page
*/
if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
set_pte_at_notify(mm, addr, ptep, entry);
goto out_unlock;
}
entry = pte_wrprotect(entry);
set_pte_at_notify(mm, addr, ptep, entry);
}
*orig_pte = *ptep;
err = 0;
out_unlock:
pte_unmap_unlock(ptep, ptl);
out:
return err;
}
/**
* replace_page - replace page in vma by new ksm page
* @vma: vma that holds the pte pointing to oldpage
* @oldpage: the page we are replacing by newpage
* @newpage: the ksm page we replace oldpage by
* @orig_pte: the original value of the pte
*
* Returns 0 on success, -EFAULT on failure.
*/
static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
struct page *newpage, pte_t orig_pte)
{
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *ptep;
spinlock_t *ptl;
unsigned long addr;
pgprot_t prot;
int err = -EFAULT;
prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
addr = page_address_in_vma(oldpage, vma);
if (addr == -EFAULT)
goto out;
pgd = pgd_offset(mm, addr);
if (!pgd_present(*pgd))
goto out;
pud = pud_offset(pgd, addr);
if (!pud_present(*pud))
goto out;
pmd = pmd_offset(pud, addr);
if (!pmd_present(*pmd))
goto out;
ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
if (!pte_same(*ptep, orig_pte)) {
pte_unmap_unlock(ptep, ptl);
goto out;
}
get_page(newpage);
page_add_ksm_rmap(newpage);
flush_cache_page(vma, addr, pte_pfn(*ptep));
ptep_clear_flush(vma, addr, ptep);
set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
page_remove_rmap(oldpage);
put_page(oldpage);
pte_unmap_unlock(ptep, ptl);
err = 0;
out:
return err;
}
/*
* try_to_merge_one_page - take two pages and merge them into one
* @vma: the vma that hold the pte pointing into oldpage
* @oldpage: the page that we want to replace with newpage
* @newpage: the page that we want to map instead of oldpage
*
* Note:
* oldpage should be a PageAnon page, while newpage should be a PageKsm page,
* or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
*
* This function returns 0 if the pages were merged, -EFAULT otherwise.
*/
static int try_to_merge_one_page(struct vm_area_struct *vma,
struct page *oldpage,
struct page *newpage)
{
pte_t orig_pte = __pte(0);
int err = -EFAULT;
if (!(vma->vm_flags & VM_MERGEABLE))
goto out;
if (!PageAnon(oldpage))
goto out;
get_page(newpage);
get_page(oldpage);
/*
* We need the page lock to read a stable PageSwapCache in
* write_protect_page(). We use trylock_page() instead of
* lock_page() because we don't want to wait here - we
* prefer to continue scanning and merging different pages,
* then come back to this page when it is unlocked.
*/
if (!trylock_page(oldpage))
goto out_putpage;
/*
* If this anonymous page is mapped only here, its pte may need
* to be write-protected. If it's mapped elsewhere, all of its
* ptes are necessarily already write-protected. But in either
* case, we need to lock and check page_count is not raised.
*/
if (write_protect_page(vma, oldpage, &orig_pte)) {
unlock_page(oldpage);
goto out_putpage;
}
unlock_page(oldpage);
if (pages_identical(oldpage, newpage))
err = replace_page(vma, oldpage, newpage, orig_pte);
out_putpage:
put_page(oldpage);
put_page(newpage);
out:
return err;
}
/*
* try_to_merge_two_pages - take two identical pages and prepare them
* to be merged into one page.
*
* This function returns 0 if we successfully mapped two identical pages
* into one page, -EFAULT otherwise.
*
* Note that this function allocates a new kernel page: if one of the pages
* is already a ksm page, try_to_merge_with_ksm_page should be used.
*/
static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
struct page *page1, struct mm_struct *mm2,
unsigned long addr2, struct page *page2)
{
struct vm_area_struct *vma;
struct page *kpage;
int err = -EFAULT;
/*
* The number of nodes in the stable tree
* is the number of kernel pages that we hold.
*/
if (ksm_max_kernel_pages &&
ksm_max_kernel_pages <= ksm_pages_shared)
return err;
kpage = alloc_page(GFP_HIGHUSER);
if (!kpage)
return err;
down_read(&mm1->mmap_sem);
vma = find_vma(mm1, addr1);
if (!vma || vma->vm_start > addr1) {
put_page(kpage);
up_read(&mm1->mmap_sem);
return err;
}
copy_user_highpage(kpage, page1, addr1, vma);
err = try_to_merge_one_page(vma, page1, kpage);
up_read(&mm1->mmap_sem);
if (!err) {
down_read(&mm2->mmap_sem);
vma = find_vma(mm2, addr2);
if (!vma || vma->vm_start > addr2) {
put_page(kpage);
up_read(&mm2->mmap_sem);
break_cow(mm1, addr1);
return -EFAULT;
}
err = try_to_merge_one_page(vma, page2, kpage);
up_read(&mm2->mmap_sem);
/*
* If the second try_to_merge_one_page failed, we have a
* ksm page with just one pte pointing to it, so break it.
*/
if (err)
break_cow(mm1, addr1);
else
ksm_pages_sharing += 2;
}
put_page(kpage);
return err;
}
/*
* try_to_merge_with_ksm_page - like try_to_merge_two_pages,
* but no new kernel page is allocated: kpage must already be a ksm page.
*/
static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
unsigned long addr1,
struct page *page1,
struct page *kpage)
{
struct vm_area_struct *vma;
int err = -EFAULT;
down_read(&mm1->mmap_sem);
vma = find_vma(mm1, addr1);
if (!vma || vma->vm_start > addr1) {
up_read(&mm1->mmap_sem);
return err;
}
err = try_to_merge_one_page(vma, page1, kpage);
up_read(&mm1->mmap_sem);
if (!err)
ksm_pages_sharing++;
return err;
}
/*
* stable_tree_search - search page inside the stable tree
* @page: the page that we are searching identical pages to.
* @page2: pointer into identical page that we are holding inside the stable
* tree that we have found.
* @rmap_item: the reverse mapping item
*
* This function checks if there is a page inside the stable tree
* with identical content to the page that we are scanning right now.
*
* This function return rmap_item pointer to the identical item if found,
* NULL otherwise.
*/
static struct rmap_item *stable_tree_search(struct page *page,
struct page **page2,
struct rmap_item *rmap_item)
{
struct rb_node *node = root_stable_tree.rb_node;
while (node) {
struct rmap_item *tree_rmap_item, *next_rmap_item;
int ret;
tree_rmap_item = rb_entry(node, struct rmap_item, node);
while (tree_rmap_item) {
BUG_ON(!in_stable_tree(tree_rmap_item));
cond_resched();
page2[0] = get_ksm_page(tree_rmap_item);
if (page2[0])
break;
next_rmap_item = tree_rmap_item->next;
remove_rmap_item_from_tree(tree_rmap_item);
tree_rmap_item = next_rmap_item;
}
if (!tree_rmap_item)
return NULL;
ret = memcmp_pages(page, page2[0]);
if (ret < 0) {
put_page(page2[0]);
node = node->rb_left;
} else if (ret > 0) {
put_page(page2[0]);
node = node->rb_right;
} else {
return tree_rmap_item;
}
}
return NULL;
}
/*
* stable_tree_insert - insert rmap_item pointing to new ksm page
* into the stable tree.
*
* @page: the page that we are searching identical page to inside the stable
* tree.
* @rmap_item: pointer to the reverse mapping item.
*
* This function returns rmap_item if success, NULL otherwise.
*/
static struct rmap_item *stable_tree_insert(struct page *page,
struct rmap_item *rmap_item)
{
struct rb_node **new = &root_stable_tree.rb_node;
struct rb_node *parent = NULL;
while (*new) {
struct rmap_item *tree_rmap_item, *next_rmap_item;
struct page *tree_page;
int ret;
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
while (tree_rmap_item) {
BUG_ON(!in_stable_tree(tree_rmap_item));
cond_resched();
tree_page = get_ksm_page(tree_rmap_item);
if (tree_page)
break;
next_rmap_item = tree_rmap_item->next;
remove_rmap_item_from_tree(tree_rmap_item);
tree_rmap_item = next_rmap_item;
}
if (!tree_rmap_item)
return NULL;
ret = memcmp_pages(page, tree_page);
put_page(tree_page);
parent = *new;
if (ret < 0)
new = &parent->rb_left;
else if (ret > 0)
new = &parent->rb_right;
else {
/*
* It is not a bug that stable_tree_search() didn't
* find this node: because at that time our page was
* not yet write-protected, so may have changed since.
*/
return NULL;
}
}
ksm_pages_shared++;
rmap_item->address |= NODE_FLAG | STABLE_FLAG;
rmap_item->next = NULL;
rb_link_node(&rmap_item->node, parent, new);
rb_insert_color(&rmap_item->node, &root_stable_tree);
return rmap_item;
}
/*
* unstable_tree_search_insert - search and insert items into the unstable tree.
*
* @page: the page that we are going to search for identical page or to insert
* into the unstable tree
* @page2: pointer into identical page that was found inside the unstable tree
* @rmap_item: the reverse mapping item of page
*
* This function searches for a page in the unstable tree identical to the
* page currently being scanned; and if no identical page is found in the
* tree, we insert rmap_item as a new object into the unstable tree.
*
* This function returns pointer to rmap_item found to be identical
* to the currently scanned page, NULL otherwise.
*
* This function does both searching and inserting, because they share
* the same walking algorithm in an rbtree.
*/
static struct rmap_item *unstable_tree_search_insert(struct page *page,
struct page **page2,
struct rmap_item *rmap_item)
{
struct rb_node **new = &root_unstable_tree.rb_node;
struct rb_node *parent = NULL;
while (*new) {
struct rmap_item *tree_rmap_item;
int ret;
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
page2[0] = get_mergeable_page(tree_rmap_item);
if (!page2[0])
return NULL;
/*
* Don't substitute an unswappable ksm page
* just for one good swappable forked page.
*/
if (page == page2[0]) {
put_page(page2[0]);
return NULL;
}
ret = memcmp_pages(page, page2[0]);
parent = *new;
if (ret < 0) {
put_page(page2[0]);
new = &parent->rb_left;
} else if (ret > 0) {
put_page(page2[0]);
new = &parent->rb_right;
} else {
return tree_rmap_item;
}
}
rmap_item->address |= NODE_FLAG;
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
rb_link_node(&rmap_item->node, parent, new);
rb_insert_color(&rmap_item->node, &root_unstable_tree);
return NULL;
}
/*
* stable_tree_append - add another rmap_item to the linked list of
* rmap_items hanging off a given node of the stable tree, all sharing
* the same ksm page.
*/
static void stable_tree_append(struct rmap_item *rmap_item,
struct rmap_item *tree_rmap_item)
{
rmap_item->next = tree_rmap_item->next;
rmap_item->prev = tree_rmap_item;
if (tree_rmap_item->next)
tree_rmap_item->next->prev = rmap_item;
tree_rmap_item->next = rmap_item;
rmap_item->address |= STABLE_FLAG;
}
/*
* cmp_and_merge_page - take a page computes its hash value and check if there
* is similar hash value to different page,
* in case we find that there is similar hash to different page we call to
* try_to_merge_two_pages().
*
* @page: the page that we are searching identical page to.
* @rmap_item: the reverse mapping into the virtual address of this page
*/
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
{
struct page *page2[1];
struct rmap_item *tree_rmap_item;
unsigned int checksum;
int err;
if (in_stable_tree(rmap_item))
remove_rmap_item_from_tree(rmap_item);
/* We first start with searching the page inside the stable tree */
tree_rmap_item = stable_tree_search(page, page2, rmap_item);
if (tree_rmap_item) {
if (page == page2[0]) { /* forked */
ksm_pages_sharing++;
err = 0;
} else
err = try_to_merge_with_ksm_page(rmap_item->mm,
rmap_item->address,
page, page2[0]);
put_page(page2[0]);
if (!err) {
/*
* The page was successfully merged:
* add its rmap_item to the stable tree.
*/
stable_tree_append(rmap_item, tree_rmap_item);
}
return;
}
/*
* A ksm page might have got here by fork, but its other
* references have already been removed from the stable tree.
*/
if (PageKsm(page))
break_cow(rmap_item->mm, rmap_item->address);
/*
* In case the hash value of the page was changed from the last time we
* have calculated it, this page to be changed frequely, therefore we
* don't want to insert it to the unstable tree, and we don't want to
* waste our time to search if there is something identical to it there.
*/
checksum = calc_checksum(page);
if (rmap_item->oldchecksum != checksum) {
rmap_item->oldchecksum = checksum;
return;
}
tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
if (tree_rmap_item) {
err = try_to_merge_two_pages(rmap_item->mm,
rmap_item->address, page,
tree_rmap_item->mm,
tree_rmap_item->address, page2[0]);
/*
* As soon as we merge this page, we want to remove the
* rmap_item of the page we have merged with from the unstable
* tree, and insert it instead as new node in the stable tree.
*/
if (!err) {
rb_erase(&tree_rmap_item->node, &root_unstable_tree);
tree_rmap_item->address &= ~NODE_FLAG;
/*
* If we fail to insert the page into the stable tree,
* we will have 2 virtual addresses that are pointing
* to a ksm page left outside the stable tree,
* in which case we need to break_cow on both.
*/
if (stable_tree_insert(page2[0], tree_rmap_item))
stable_tree_append(rmap_item, tree_rmap_item);
else {
break_cow(tree_rmap_item->mm,
tree_rmap_item->address);
break_cow(rmap_item->mm, rmap_item->address);
ksm_pages_sharing -= 2;
}
}
put_page(page2[0]);
}
}
static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
struct list_head *cur,
unsigned long addr)
{
struct rmap_item *rmap_item;
while (cur != &mm_slot->rmap_list) {
rmap_item = list_entry(cur, struct rmap_item, link);
if ((rmap_item->address & PAGE_MASK) == addr) {
if (!in_stable_tree(rmap_item))
remove_rmap_item_from_tree(rmap_item);
return rmap_item;
}
if (rmap_item->address > addr)
break;
cur = cur->next;
remove_rmap_item_from_tree(rmap_item);
list_del(&rmap_item->link);
free_rmap_item(rmap_item);
}
rmap_item = alloc_rmap_item();
if (rmap_item) {
/* It has already been zeroed */
rmap_item->mm = mm_slot->mm;
rmap_item->address = addr;
list_add_tail(&rmap_item->link, cur);
}
return rmap_item;
}
static struct rmap_item *scan_get_next_rmap_item(struct page **page)
{
struct mm_struct *mm;
struct mm_slot *slot;
struct vm_area_struct *vma;
struct rmap_item *rmap_item;
if (list_empty(&ksm_mm_head.mm_list))
return NULL;
slot = ksm_scan.mm_slot;
if (slot == &ksm_mm_head) {
root_unstable_tree = RB_ROOT;
spin_lock(&ksm_mmlist_lock);
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.mm_slot = slot;
spin_unlock(&ksm_mmlist_lock);
next_mm:
ksm_scan.address = 0;
ksm_scan.rmap_item = list_entry(&slot->rmap_list,
struct rmap_item, link);
}
mm = slot->mm;
down_read(&mm->mmap_sem);
for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) {
if (!(vma->vm_flags & VM_MERGEABLE))
continue;
if (ksm_scan.address < vma->vm_start)
ksm_scan.address = vma->vm_start;
if (!vma->anon_vma)
ksm_scan.address = vma->vm_end;
while (ksm_scan.address < vma->vm_end) {
*page = follow_page(vma, ksm_scan.address, FOLL_GET);
if (*page && PageAnon(*page)) {
flush_anon_page(vma, *page, ksm_scan.address);
flush_dcache_page(*page);
rmap_item = get_next_rmap_item(slot,
ksm_scan.rmap_item->link.next,
ksm_scan.address);
if (rmap_item) {
ksm_scan.rmap_item = rmap_item;
ksm_scan.address += PAGE_SIZE;
} else
put_page(*page);
up_read(&mm->mmap_sem);
return rmap_item;
}
if (*page)
put_page(*page);
ksm_scan.address += PAGE_SIZE;
cond_resched();
}
}
if (!ksm_scan.address) {
/*
* We've completed a full scan of all vmas, holding mmap_sem
* throughout, and found no VM_MERGEABLE: so do the same as
* __ksm_exit does to remove this mm from all our lists now.
*/
remove_mm_from_lists(mm);
up_read(&mm->mmap_sem);
slot = ksm_scan.mm_slot;
if (slot != &ksm_mm_head)
goto next_mm;
return NULL;
}
/*
* Nuke all the rmap_items that are above this current rmap:
* because there were no VM_MERGEABLE vmas with such addresses.
*/
remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
up_read(&mm->mmap_sem);
spin_lock(&ksm_mmlist_lock);
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.mm_slot = slot;
spin_unlock(&ksm_mmlist_lock);
/* Repeat until we've completed scanning the whole list */
if (slot != &ksm_mm_head)
goto next_mm;
/*
* Bump seqnr here rather than at top, so that __ksm_exit
* can skip rb_erase on unstable tree until we run again.
*/
ksm_scan.seqnr++;
return NULL;
}
/**
* ksm_do_scan - the ksm scanner main worker function.
* @scan_npages - number of pages we want to scan before we return.
*/
static void ksm_do_scan(unsigned int scan_npages)
{
struct rmap_item *rmap_item;
struct page *page;
while (scan_npages--) {
cond_resched();
rmap_item = scan_get_next_rmap_item(&page);
if (!rmap_item)
return;
if (!PageKsm(page) || !in_stable_tree(rmap_item))
cmp_and_merge_page(page, rmap_item);
put_page(page);
}
}
static int ksm_scan_thread(void *nothing)
{
set_user_nice(current, 5);
while (!kthread_should_stop()) {
if (ksm_run & KSM_RUN_MERGE) {
mutex_lock(&ksm_thread_mutex);
ksm_do_scan(ksm_thread_pages_to_scan);
mutex_unlock(&ksm_thread_mutex);
schedule_timeout_interruptible(
msecs_to_jiffies(ksm_thread_sleep_millisecs));
} else {
wait_event_interruptible(ksm_thread_wait,
(ksm_run & KSM_RUN_MERGE) ||
kthread_should_stop());
}
}
return 0;
}
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
unsigned long end, int advice, unsigned long *vm_flags)
{
struct mm_struct *mm = vma->vm_mm;
switch (advice) {
case MADV_MERGEABLE:
/*
* Be somewhat over-protective for now!
*/
if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
VM_PFNMAP | VM_IO | VM_DONTEXPAND |
VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
VM_MIXEDMAP | VM_SAO))
return 0; /* just ignore the advice */
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
if (__ksm_enter(mm) < 0)
return -EAGAIN;
*vm_flags |= VM_MERGEABLE;
break;
case MADV_UNMERGEABLE:
if (!(*vm_flags & VM_MERGEABLE))
return 0; /* just ignore the advice */
if (vma->anon_vma)
unmerge_ksm_pages(vma, start, end);
*vm_flags &= ~VM_MERGEABLE;
break;
}
return 0;
}
int __ksm_enter(struct mm_struct *mm)
{
struct mm_slot *mm_slot = alloc_mm_slot();
if (!mm_slot)
return -ENOMEM;
spin_lock(&ksm_mmlist_lock);
insert_to_mm_slots_hash(mm, mm_slot);
/*
* Insert just behind the scanning cursor, to let the area settle
* down a little; when fork is followed by immediate exec, we don't
* want ksmd to waste time setting up and tearing down an rmap_list.
*/
list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
spin_unlock(&ksm_mmlist_lock);
set_bit(MMF_VM_MERGEABLE, &mm->flags);
return 0;
}
void __ksm_exit(struct mm_struct *mm)
{
/*
* This process is exiting: doesn't hold and doesn't need mmap_sem;
* but we do need to exclude ksmd and other exiters while we modify
* the various lists and trees.
*/
mutex_lock(&ksm_thread_mutex);
remove_mm_from_lists(mm);
mutex_unlock(&ksm_thread_mutex);
}
#define KSM_ATTR_RO(_name) \
static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
#define KSM_ATTR(_name) \
static struct kobj_attribute _name##_attr = \
__ATTR(_name, 0644, _name##_show, _name##_store)
static ssize_t sleep_millisecs_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
}
static ssize_t sleep_millisecs_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
unsigned long msecs;
int err;
err = strict_strtoul(buf, 10, &msecs);
if (err || msecs > UINT_MAX)
return -EINVAL;
ksm_thread_sleep_millisecs = msecs;
return count;
}
KSM_ATTR(sleep_millisecs);
static ssize_t pages_to_scan_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
}
static ssize_t pages_to_scan_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long nr_pages;
err = strict_strtoul(buf, 10, &nr_pages);
if (err || nr_pages > UINT_MAX)
return -EINVAL;
ksm_thread_pages_to_scan = nr_pages;
return count;
}
KSM_ATTR(pages_to_scan);
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
return sprintf(buf, "%u\n", ksm_run);
}
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long flags;
err = strict_strtoul(buf, 10, &flags);
if (err || flags > UINT_MAX)
return -EINVAL;
if (flags > KSM_RUN_UNMERGE)
return -EINVAL;
/*
* KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
* KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
* breaking COW to free the unswappable pages_shared (but leaves
* mm_slots on the list for when ksmd may be set running again).
*/
mutex_lock(&ksm_thread_mutex);
if (ksm_run != flags) {
ksm_run = flags;
if (flags & KSM_RUN_UNMERGE)
unmerge_and_remove_all_rmap_items();
}
mutex_unlock(&ksm_thread_mutex);
if (flags & KSM_RUN_MERGE)
wake_up_interruptible(&ksm_thread_wait);
return count;
}
KSM_ATTR(run);
static ssize_t max_kernel_pages_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long nr_pages;
err = strict_strtoul(buf, 10, &nr_pages);
if (err)
return -EINVAL;
ksm_max_kernel_pages = nr_pages;
return count;
}
static ssize_t max_kernel_pages_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
}
KSM_ATTR(max_kernel_pages);
static ssize_t pages_shared_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%lu\n", ksm_pages_shared);
}
KSM_ATTR_RO(pages_shared);
static ssize_t pages_sharing_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%lu\n",
ksm_pages_sharing - ksm_pages_shared);
}
KSM_ATTR_RO(pages_sharing);
static struct attribute *ksm_attrs[] = {
&sleep_millisecs_attr.attr,
&pages_to_scan_attr.attr,
&run_attr.attr,
&max_kernel_pages_attr.attr,
&pages_shared_attr.attr,
&pages_sharing_attr.attr,
NULL,
};
static struct attribute_group ksm_attr_group = {
.attrs = ksm_attrs,
.name = "ksm",
};
static int __init ksm_init(void)
{
struct task_struct *ksm_thread;
int err;
err = ksm_slab_init();
if (err)
goto out;
err = mm_slots_hash_init();
if (err)
goto out_free1;
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
if (IS_ERR(ksm_thread)) {
printk(KERN_ERR "ksm: creating kthread failed\n");
err = PTR_ERR(ksm_thread);
goto out_free2;
}
err = sysfs_create_group(mm_kobj, &ksm_attr_group);
if (err) {
printk(KERN_ERR "ksm: register sysfs failed\n");
goto out_free3;
}
return 0;
out_free3:
kthread_stop(ksm_thread);
out_free2:
mm_slots_hash_free();
out_free1:
ksm_slab_free();
out:
return err;
}
module_init(ksm_init)