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Commit ba6f0ff3 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
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ksm: fix ksm swapin time optimization 



The new anon-vma code, was suboptimal and it lead to erratic invocation of
ksm_does_need_to_copy.  That leads to host hangs or guest vnc lockup, or
weird behavior.  It's unclear why ksm_does_need_to_copy is unstable but
the point is that when KSM is not in use, ksm_does_need_to_copy must never
run or we bounce pages for no good reason.  I suspect the same hangs will
happen with KVM swaps.  But this at least fixes the regression in the
new-anon-vma code and it only let KSM bugs triggers when KSM is in use.

The code in do_swap_page likely doesn't cope well with a not-swapcache,
especially the memcg code.

Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Cc: Izik Eidus <ieidus@yahoo.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 26ba0cb6

include/linux/ksm.h

+1 −1
Original line number Diff line number Diff line
@@ -78,7 +78,7 @@ static inline struct page *ksm_might_need_to_copy(struct page *page, 
	struct anon_vma *anon_vma = page_anon_vma(page);



	if (!anon_vma ||

	    (anon_vma == vma->anon_vma &&

	    (anon_vma->root == vma->anon_vma->root &&

	     page->index == linear_page_index(vma, address)))

		return page;