From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752394Ab1LGJVS (ORCPT ); Wed, 7 Dec 2011 04:21:18 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:45585 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751717Ab1LGJVQ (ORCPT ); Wed, 7 Dec 2011 04:21:16 -0500 Date: Wed, 7 Dec 2011 10:21:07 +0100 From: Johannes Weiner To: KAMEZAWA Hiroyuki Cc: "linux-kernel@vger.kernel.org" , Miklos Szeredi , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , cgroups@vger.kernel.org, Michal Hocko , Hugh Dickins Subject: Re: [BUGFIX][PATCH] add mem_cgroup_replace_page_cache. Message-ID: <20111207092107.GB12673@cmpxchg.org> References: <20111206123923.1432ab52.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111206123923.1432ab52.kamezawa.hiroyu@jp.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 06, 2011 at 12:39:23PM +0900, KAMEZAWA Hiroyuki wrote: > > Hm, is this too naive ? better idea is welcome. > == > >From 33638351c5cd28af9f47f9ab1c44eeb1f63d9964 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki > Date: Tue, 6 Dec 2011 12:32:32 +0900 > Subject: [PATCH] memcg: add mem_cgroup_replace_page_cache() for fixing LRU issue. > > commit ef6a3c6311 adds a function replace_page_cache_page(). This > function replaces a page in radix-tree with a new page. > At doing this, memory cgroup need to fix up the accounting information. > memcg need to check PCG_USED bit etc. > > In some(many?) case, 'newpage' is on LRU before calling replace_page_cache(). > So, memcg's LRU accounting information should be fixed, too. > > This patch adds mem_cgroup_replace_page_cache() and removing old hooks. > In that function, old pages will be unaccounted without touching res_counter > and new page will be accounted to the memcg (of old page). At overwriting > pc->mem_cgroup of newpage, take zone->lru_lock and avoid race with > LRU handling. > > Background: > replace_page_cache_page() is called by FUSE code in its splice() handling. > Here, 'newpage' is replacing oldpage but this newpage is not a newly allocated > page and may be on LRU. LRU mis-accounting will be critical for memory cgroup > because rmdir() checks the whole LRU is empty and there is no account leak. > If a page is on the other LRU than it should be, rmdir() will fail. > > Signed-off-by: KAMEZAWA Hiroyuki I think this is okay. It's a tiny bit unfortunate that the migration code is more or less duplicated with some optimizations, but I fear the other solutions would be more complex and thus not adequate as a bug fix. Acked-by: Johannes Weiner