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Commit 26465d3e authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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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: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: default avatarIzik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 473b0ce4

mm/ksm.c

+8 −0
Original line number Diff line number Diff line
@@ -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);

	}

}