From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752198AbaJSPbz (ORCPT ); Sun, 19 Oct 2014 11:31:55 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:42274 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751525AbaJSPbw (ORCPT ); Sun, 19 Oct 2014 11:31:52 -0400 From: Johannes Weiner To: Andrew Morton Cc: Hugh Dickins , Michal Hocko , 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 Message-Id: <1413732647-16043-1-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 2.1.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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