Commit 26465d3e authored Sep 21, 2009 by Hugh Dickins Committed by Linus Torvalds Sep 22, 2009

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>

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);
		}
		}

Admin message