Messages in this thread Patch in this message | | | Date | Mon, 3 Aug 2009 13:12:59 +0100 (BST) | From | Hugh Dickins <> | Subject | [PATCH 4/12] ksm: break cow once unshared |
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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> ---
mm/ksm.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- ksm3/mm/ksm.c 2009-08-02 13:49:51.000000000 +0100 +++ ksm4/mm/ksm.c 2009-08-02 13:49:59.000000000 +0100 @@ -1275,6 +1275,14 @@ static void ksm_do_scan(unsigned int sca 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); } }
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