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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
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@@ -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 */