From db114b83ab6064d9b1d6ec5650e096c89bd95e25 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 14 Dec 2009 17:59:25 -0800 Subject: 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 Cc: Izik Eidus Cc: Andrea Arcangeli Cc: Chris Wright Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/rmap.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'include') diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 0b4913a4a344..980094a527ee 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -26,6 +26,9 @@ */ struct anon_vma { spinlock_t lock; /* Serialize access to vma list */ +#ifdef CONFIG_KSM + atomic_t ksm_refcount; +#endif /* * NOTE: the LSB of the head.next is set by * mm_take_all_locks() _after_ taking the above lock. So the @@ -38,6 +41,26 @@ struct anon_vma { }; #ifdef CONFIG_MMU +#ifdef CONFIG_KSM +static inline void ksm_refcount_init(struct anon_vma *anon_vma) +{ + atomic_set(&anon_vma->ksm_refcount, 0); +} + +static inline int ksm_refcount(struct anon_vma *anon_vma) +{ + return atomic_read(&anon_vma->ksm_refcount); +} +#else +static inline void ksm_refcount_init(struct anon_vma *anon_vma) +{ +} + +static inline int ksm_refcount(struct anon_vma *anon_vma) +{ + return 0; +} +#endif /* CONFIG_KSM */ static inline struct anon_vma *page_anon_vma(struct page *page) { @@ -70,6 +93,7 @@ void __anon_vma_merge(struct vm_area_struct *, struct vm_area_struct *); void anon_vma_unlink(struct vm_area_struct *); void anon_vma_link(struct vm_area_struct *); void __anon_vma_link(struct vm_area_struct *); +void anon_vma_free(struct anon_vma *); /* * rmap interfaces called when adding or removing pte of page -- cgit v1.2.3