path: root/include/linux/ksm.h
diff options
authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-12-14 17:59:21 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-15 08:53:19 -0800
commit08beca44dfb0ab008e365163df70dbd302ae1508 (patch)
tree33f3ddf5460e139bd7fd37e8c08026a7d852c3da /include/linux/ksm.h
parent7b6ba2c7d3baf8cd9f888e05563dcc32e368baab (diff)
ksm: stable_node point to page and back
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>
Diffstat (limited to 'include/linux/ksm.h')
1 files changed, 17 insertions, 7 deletions
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 1401a313fa77..ef55ce14a2ce 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -12,6 +12,8 @@
#include <linux/sched.h>
#include <linux/vmstat.h>
+struct stable_node;
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)
- * 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 +
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 */