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Message-Id: <1413732647-16043-1-git-send-email-hannes@cmpxchg.org> Date: Sun, 19 Oct 2014 11:30:47 -0400 From: Johannes Weiner <hannes@...xchg.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [patch] mm: memcontrol: clarify migration where old page is uncharged 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@...xchg.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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