From 2919bfd0758257c469abef8c26c3e516bbebb851 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 13 Jan 2011 15:47:29 -0800 Subject: [PATCH] ksm: drain pagevecs to lru It was hard to explain the page counts which were causing new LTP tests of KSM to fail: we need to drain the per-cpu pagevecs to LRU occasionally. Signed-off-by: Hugh Dickins Reported-by: CAI Qian Cc:Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/ksm.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index 33781de0b6bf..c2b2a94f9d67 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1296,6 +1296,18 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) slot = ksm_scan.mm_slot; if (slot == &ksm_mm_head) { + /* + * A number of pages can hang around indefinitely on per-cpu + * pagevecs, raised page count preventing write_protect_page + * from merging them. Though it doesn't really matter much, + * it is puzzling to see some stuck in pages_volatile until + * other activity jostles them out, and they also prevented + * LTP's KSM test from succeeding deterministically; so drain + * them here (here rather than on entry to ksm_do_scan(), + * so we don't IPI too often when pages_to_scan is set low). + */ + lru_add_drain_all(); + root_unstable_tree = RB_ROOT; spin_lock(&ksm_mmlist_lock);