Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757832Ab0FPAW2 (ORCPT ); Tue, 15 Jun 2010 20:22:28 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:47347 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755280Ab0FPAW1 (ORCPT ); Tue, 15 Jun 2010 20:22:27 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Wed, 16 Jun 2010 09:17:55 +0900 From: KAMEZAWA Hiroyuki To: Mel Gorman Cc: Rik van Riel , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Chris Mason , Nick Piggin , Johannes Weiner , Christoph Hellwig , Andrew Morton Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim Message-Id: <20100616091755.7121c7d3.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100615141601.GL26788@csn.ul.ie> References: <1276514273-27693-1-git-send-email-mel@csn.ul.ie> <1276514273-27693-13-git-send-email-mel@csn.ul.ie> <4C16A567.4080000@redhat.com> <20100615114510.GE26788@csn.ul.ie> <4C17815A.8080402@redhat.com> <20100615135928.GK26788@csn.ul.ie> <4C178868.2010002@redhat.com> <20100615141601.GL26788@csn.ul.ie> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.2 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1848 Lines: 49 On Tue, 15 Jun 2010 15:16:01 +0100 Mel Gorman wrote: > On Tue, Jun 15, 2010 at 10:04:24AM -0400, Rik van Riel wrote: > > On 06/15/2010 09:59 AM, Mel Gorman wrote: > >> On Tue, Jun 15, 2010 at 09:34:18AM -0400, Rik van Riel wrote: > >>> On 06/15/2010 07:45 AM, Mel Gorman wrote: > > > >>>>>> > >>>>>> +/* kswapd and memcg can writeback as they are unlikely to overflow stack */ > >>>>>> +static inline bool reclaim_can_writeback(struct scan_control *sc) > >>>>>> +{ > >>>>>> + return current_is_kswapd() || sc->mem_cgroup != NULL; > >>>>>> +} > > > >>> If direct reclaim can overflow the stack, so can direct > >>> memcg reclaim. That means this patch does not solve the > >>> stack overflow, while admitting that we do need the > >>> ability to get specific pages flushed to disk from the > >>> pageout code. > >>> > >> > >> What path is taken with memcg != NULL that could overflow the stack? I > >> couldn't spot one but mm/memcontrol.c is a bit tangled so finding all > >> its use cases is tricky. The critical path I had in mind though was > >> direct reclaim and for that path, memcg == NULL or did I miss something? > > > > mem_cgroup_hierarchical_reclaim -> try_to_free_mem_cgroup_pages > > > > But in turn, where is mem_cgroup_hierarchical_reclaim called from direct > reclaim? It appears to be only called from the fault path or as a result > of the memcg changing size. > yes. It's only called from - page fault - add_to_page_cache() I think we'll see no stack problem. Now, memcg doesn't wakeup kswapd for reclaiming memory, it needs direct writeback. Thanks, -Kame -- 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/