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authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-09-21 17:02:12 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-22 07:17:32 -0700
commit26465d3ea5a62d59efb3796b9e0e2b0656d02cb1 (patch)
tree40644bae6d246a1ee0d38b98a5281a3a879725a1 /mm/ksm.c
parentksm: pages_unshared and pages_volatile (diff)
downloadlinux-dev-26465d3ea5a62d59efb3796b9e0e2b0656d02cb1.tar.xz
linux-dev-26465d3ea5a62d59efb3796b9e0e2b0656d02cb1.zip
ksm: break cow once unshared
We kept agreeing not to bother about the unswappable shared KSM pages which later become unshared by others: observation suggests they're not a significant proportion. But they are disadvantageous, and it is easier to break COW to replace them by swappable pages, than offer statistics to show that they don't matter; then we can stop worrying about them. Doing this in ksm_do_scan, they don't go through cmp_and_merge_page on this pass: give them a good chance of getting into the unstable tree on the next pass, or back into the stable, by computing checksum now. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Acked-by: Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to '')
-rw-r--r--mm/ksm.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index 9f8f0523562b..81f692e836db 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1268,6 +1268,14 @@ static void ksm_do_scan(unsigned int scan_npages)
return;
if (!PageKsm(page) || !in_stable_tree(rmap_item))
cmp_and_merge_page(page, rmap_item);
+ else if (page_mapcount(page) == 1) {
+ /*
+ * Replace now-unshared ksm page by ordinary page.
+ */
+ break_cow(rmap_item->mm, rmap_item->address);
+ remove_rmap_item_from_tree(rmap_item);
+ rmap_item->oldchecksum = calc_checksum(page);
+ }
put_page(page);
}
}