From: Johannes Weiner <hannes@cmpxchg.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@suse.cz>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [patch] mm: memcontrol: clarify migration where old page is uncharged
Date: Sun, 19 Oct 2014 11:30:47 -0400 [thread overview]
Message-ID: <1413732647-16043-1-git-send-email-hannes@cmpxchg.org> (raw)
Better explain re-entrant migration when compaction races with
reclaim, and also mention swapcache readahead pages as possible
uncharged migration sources.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/memcontrol.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fc1d7ca96b9d..76892eb89d26 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6166,7 +6166,12 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
if (PageCgroupUsed(pc))
return;
- /* Re-entrant migration: old page already uncharged? */
+ /*
+ * Swapcache readahead pages can get migrated before being
+ * charged, and migration from compaction can happen to an
+ * uncharged page when the PFN walker finds a page that
+ * reclaim just put back on the LRU but has not released yet.
+ */
pc = lookup_page_cgroup(oldpage);
if (!PageCgroupUsed(pc))
return;
--
2.1.2
next reply other threads:[~2014-10-19 15:31 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-19 15:30 Johannes Weiner [this message]
2014-10-20 19:45 ` [patch] mm: memcontrol: clarify migration where old page is uncharged Michal Hocko
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