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.
Reported-by: CAI Qian <caiqian@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/ksm.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- 2.6.37/mm/ksm.c 2010-12-24 19:31:45.000000000 -0800
+++ linux/mm/ksm.c 2011-01-02 15:06:52.000000000 -0800
@@ -1247,6 +1247,18 @@ static struct rmap_item *scan_get_next_r
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);
--
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