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>
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 1401a31..ef55ce1 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;
+
#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 @@
/*
* 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 @@
(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 */