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authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-12-15 04:59:25 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-15 19:53:19 +0300
commitdb114b83ab6064d9b1d6ec5650e096c89bd95e25 (patch)
tree15e289b25fec011238f6838c6aafa1ff5e293224 /net/llc
parent5ad6468801d28c4d4ac9f48ec19297817c915f6a (diff)
downloadlinux-db114b83ab6064d9b1d6ec5650e096c89bd95e25.tar.xz
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>
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