Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753270AbZFHGyQ (ORCPT ); Mon, 8 Jun 2009 02:54:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751493AbZFHGyC (ORCPT ); Mon, 8 Jun 2009 02:54:02 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:56677 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782AbZFHGyA (ORCPT ); Mon, 8 Jun 2009 02:54:00 -0400 From: KOSAKI Motohiro To: Daisuke Nishimura Subject: Re: [PATCH mmotm] vmscan: fix may_swap handling for memcg Cc: kosaki.motohiro@jp.fujitsu.com, LKML , linux-mm , Andrew Morton , Johannes Weiner , Balbir Singh , KAMEZAWA Hiroyuki In-Reply-To: <20090608153916.3ccaeb9a.nishimura@mxp.nes.nec.co.jp> References: <20090608121848.4370.A69D9226@jp.fujitsu.com> <20090608153916.3ccaeb9a.nishimura@mxp.nes.nec.co.jp> Message-Id: <20090608154634.437F.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Mon, 8 Jun 2009 15:53:50 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2184 Lines: 56 > On Mon, 8 Jun 2009 12:20:54 +0900 (JST), KOSAKI Motohiro wrote: > > Hi > > > Hi, thank you for your comment. > > > > From: Daisuke Nishimura > > > > > > Commit 2e2e425989080cc534fc0fca154cae515f971cf5 ("vmscan,memcg: reintroduce > > > sc->may_swap) add may_swap flag and handle it at get_scan_ratio(). > > > > > > But the result of get_scan_ratio() is ignored when priority == 0, and this > > > means, when memcg hits the mem+swap limit, anon pages can be swapped > > > just in vain. Especially when memcg causes oom by mem+swap limit, > > > we can see many and many pages are swapped out. > > > > > > Instead of not scanning anon lru completely when priority == 0, this patch adds > > > a hook to handle may_swap flag in shrink_page_list() to avoid using useless swaps, > > > and calls try_to_free_swap() if needed because it can reduce > > > both mem.usage and memsw.usage if the page(SwapCache) is unused anymore. > > > > > > Such unused-but-managed-under-memcg SwapCache can be made in some paths, > > > for example trylock_page() failure in free_swap_cache(). > > > > > > Signed-off-by: Daisuke Nishimura > > > > I think root cause is following branch, right? > yes. > > > if so, Why can't we handle this issue on shrink_zone()? > > > Just because priority==0 means oom is about to happen and I don't > want to see oom if possible. > So I thought it would be better to reclaim as much pages(memsw.usage) as possible > in this case. hmmm.. In general, adding new branch to shrink_page_list() is not good idea. it can cause performance degression. Plus, it is not big problem at all. it happen only when priority==0. Definitely, priority==0 don't occur normally. and, too many recliaming pages is not only memcg issue. I don't think this patch provide generic solution. Why your test environment makes oom so frequently? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/