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ksm: stable_node point to page and back

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Add a pointer to the ksm page into struct stable_node, holding a reference
to the page while the node exists.  Put a pointer to the stable_node into
the ksm page's ->mapping.

Then we don't need get_ksm_page() while traversing the stable tree: the
page to compare against is sure to be present and correct, even if it's no
longer visible through any of its existing rmap_items.

And we can handle the forked ksm page case more efficiently: no need to
memcmp our way through the tree to find its match.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-12-14 17:59:21 -08:00 committed by Linus Torvalds
parent 7b6ba2c7d3
commit 08beca44df
2 changed files with 51 additions and 72 deletions
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24
include/linux/ksm.h
View file

@ -12,6 +12,8 @@
#include <linux/sched.h>
#include <linux/vmstat.h>
struct stable_node;
#ifdef CONFIG_KSM
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
unsigned long end, int advice, unsigned long *vm_flags);
@ -34,7 +36,8 @@ static inline void ksm_exit(struct mm_struct *mm)
/*
* A KSM page is one of those write-protected "shared pages" or "merged pages"
* which KSM maps into multiple mms, wherever identical anonymous page content
* is found in VM_MERGEABLE vmas. It's a PageAnon page, with NULL anon_vma.
* is found in VM_MERGEABLE vmas. It's a PageAnon page, pointing not to any
* anon_vma, but to that page's node of the stable tree.
*/
static inline int PageKsm(struct page *page)
{
@ -42,15 +45,22 @@ static inline int PageKsm(struct page *page)
(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
}
/*
* But we have to avoid the checking which page_add_anon_rmap() performs.
*/
static inline struct stable_node *page_stable_node(struct page *page)
{
return PageKsm(page) ? page_rmapping(page) : NULL;
}
static inline void set_page_stable_node(struct page *page,
struct stable_node *stable_node)
{
page->mapping = (void *)stable_node +
(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
}
static inline void page_add_ksm_rmap(struct page *page)
{
if (atomic_inc_and_test(&page->_mapcount)) {
page->mapping = (void *) (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
if (atomic_inc_and_test(&page->_mapcount))
__inc_zone_page_state(page, NR_ANON_PAGES);
}
}
#else /* !CONFIG_KSM */

99
mm/ksm.c
View file

@ -107,10 +107,12 @@ struct ksm_scan {
/**
* struct stable_node - node of the stable rbtree
* @page: pointer to struct page of the ksm page
* @node: rb node of this ksm page in the stable tree
* @hlist: hlist head of rmap_items using this ksm page
*/
struct stable_node {
struct page *page;
struct rb_node node;
struct hlist_head hlist;
};
@ -434,23 +436,6 @@ out: page = NULL;
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.
@ -465,6 +450,9 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
if (stable_node->hlist.first)
ksm_pages_sharing--;
else {
set_page_stable_node(stable_node->page, NULL);
put_page(stable_node->page);
rb_erase(&stable_node->node, &root_stable_tree);
free_stable_node(stable_node);
ksm_pages_shared--;
@ -740,8 +728,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
* try_to_merge_one_page - take two pages and merge them into one
* @vma: the vma that holds the pte pointing to page
* @page: the PageAnon page that we want to replace with kpage
* @kpage: the PageKsm page (or newly allocated page which page_add_ksm_rmap
* will make PageKsm) that we want to map instead of page
* @kpage: the PageKsm page that we want to map instead of page
*
* This function returns 0 if the pages were merged, -EFAULT otherwise.
*/
@ -793,6 +780,9 @@ static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
struct vm_area_struct *vma;
int err = -EFAULT;
if (page == kpage) /* ksm page forked */
return 0;
down_read(&mm->mmap_sem);
if (ksm_test_exit(mm))
goto out;
@ -846,6 +836,9 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
goto up;
copy_user_highpage(kpage, page, rmap_item->address, vma);
set_page_stable_node(kpage, NULL); /* mark it PageKsm */
err = try_to_merge_one_page(vma, page, kpage);
up:
up_read(&mm->mmap_sem);
@ -876,41 +869,31 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
* This function returns the stable tree node of identical content if found,
* NULL otherwise.
*/
static struct stable_node *stable_tree_search(struct page *page,
struct page **tree_pagep)
static struct stable_node *stable_tree_search(struct page *page)
{
struct rb_node *node = root_stable_tree.rb_node;
struct stable_node *stable_node;
stable_node = page_stable_node(page);
if (stable_node) { /* ksm page forked */
get_page(page);
return stable_node;
}
while (node) {
struct hlist_node *hlist, *hnext;
struct rmap_item *tree_rmap_item;
struct page *tree_page;
int ret;
cond_resched();
stable_node = rb_entry(node, struct stable_node, node);
hlist_for_each_entry_safe(tree_rmap_item, hlist, hnext,
&stable_node->hlist, hlist) {
BUG_ON(!in_stable_tree(tree_rmap_item));
cond_resched();
tree_page = get_ksm_page(tree_rmap_item);
if (tree_page)
break;
remove_rmap_item_from_tree(tree_rmap_item);
}
if (!hlist)
return NULL;
ret = memcmp_pages(page, tree_page);
ret = memcmp_pages(page, stable_node->page);
if (ret < 0) {
put_page(tree_page);
if (ret < 0)
node = node->rb_left;
} else if (ret > 0) {
put_page(tree_page);
else if (ret > 0)
node = node->rb_right;
} else {
*tree_pagep = tree_page;
else {
get_page(stable_node->page);
return stable_node;
}
}
@ -932,26 +915,12 @@ static struct stable_node *stable_tree_insert(struct page *kpage)
struct stable_node *stable_node;
while (*new) {
struct hlist_node *hlist, *hnext;
struct rmap_item *tree_rmap_item;
struct page *tree_page;
int ret;
cond_resched();
stable_node = rb_entry(*new, struct stable_node, node);
hlist_for_each_entry_safe(tree_rmap_item, hlist, hnext,
&stable_node->hlist, hlist) {
BUG_ON(!in_stable_tree(tree_rmap_item));
cond_resched();
tree_page = get_ksm_page(tree_rmap_item);
if (tree_page)
break;
remove_rmap_item_from_tree(tree_rmap_item);
}
if (!hlist)
return NULL;
ret = memcmp_pages(kpage, tree_page);
put_page(tree_page);
ret = memcmp_pages(kpage, stable_node->page);
parent = *new;
if (ret < 0)
@ -977,6 +946,10 @@ static struct stable_node *stable_tree_insert(struct page *kpage)
INIT_HLIST_HEAD(&stable_node->hlist);
get_page(kpage);
stable_node->page = kpage;
set_page_stable_node(kpage, stable_node);
return stable_node;
}
@ -1085,14 +1058,10 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
remove_rmap_item_from_tree(rmap_item);
/* We first start with searching the page inside the stable tree */
stable_node = stable_tree_search(page, &tree_page);
stable_node = stable_tree_search(page);
if (stable_node) {
kpage = tree_page;
if (page == kpage) /* forked */
err = 0;
else
err = try_to_merge_with_ksm_page(rmap_item,
page, kpage);
kpage = stable_node->page;
err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
if (!err) {
/*
* The page was successfully merged: