path: root/mm/rmap.c
diff options
authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-12-14 17:59:25 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-15 08:53:19 -0800
commitdb114b83ab6064d9b1d6ec5650e096c89bd95e25 (patch)
tree15e289b25fec011238f6838c6aafa1ff5e293224 /mm/rmap.c
parent5ad6468801d28c4d4ac9f48ec19297817c915f6a (diff)
ksm: hold anon_vma in rmap_item
For full functionality, page_referenced_one() and try_to_unmap_one() need to know the vma: to pass vma down to arch-dependent flushes, or to observe VM_LOCKED or VM_EXEC. But KSM keeps no record of vma: nor can it, since vmas get split and merged without its knowledge. Instead, note page's anon_vma in its rmap_item when adding to stable tree: all the vmas which might map that page are listed by its anon_vma. page_referenced_ksm() and try_to_unmap_ksm() then traverse the anon_vma, first to find the probable vma, that which matches rmap_item's mm; but if that is not enough to locate all instances, traverse again to try the others. This catches those occasions when fork has duplicated a pte of a ksm page, but ksmd has not yet come around to assign it an rmap_item. But each rmap_item in the stable tree which refers to an anon_vma needs to take a reference to it. Andrea's anon_vma design cleverly avoided a reference count (an anon_vma was free when its list of vmas was empty), but KSM now needs to add that. Is a 32-bit count sufficient? I believe so - the anon_vma is only free when both count is 0 and list is empty. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Chris Wright <chrisw@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/rmap.c')
1 files changed, 3 insertions, 2 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index 869aaa3206a..ebdf582ef18 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -68,7 +68,7 @@ static inline struct anon_vma *anon_vma_alloc(void)
return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
-static inline void anon_vma_free(struct anon_vma *anon_vma)
+void anon_vma_free(struct anon_vma *anon_vma)
kmem_cache_free(anon_vma_cachep, anon_vma);
@@ -172,7 +172,7 @@ void anon_vma_unlink(struct vm_area_struct *vma)
/* We must garbage collect the anon_vma if it's empty */
- empty = list_empty(&anon_vma->head);
+ empty = list_empty(&anon_vma->head) && !ksm_refcount(anon_vma);
if (empty)
@@ -184,6 +184,7 @@ static void anon_vma_ctor(void *data)
struct anon_vma *anon_vma = data;
+ ksm_refcount_init(anon_vma);