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: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Izik Eidus <ieidus@yahoo.com>
Cc: Avi Kivity <avi@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 43bdab7..74d691e 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -78,7 +78,7 @@
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;