From 26465d3ea5a62d59efb3796b9e0e2b0656d02cb1 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 21 Sep 2009 17:02:12 -0700 Subject: [PATCH] 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 Acked-by: Izik Eidus Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/ksm.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index 9f8f052..81f692e 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); } } -- 2.7.4