From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 744B56B01B7 for ; Tue, 15 Jun 2010 20:22:29 -0400 (EDT) Received: from m6.gw.fujitsu.co.jp ([10.0.50.76]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o5G0MPN6007483 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Wed, 16 Jun 2010 09:22:25 +0900 Received: from smail (m6 [127.0.0.1]) by outgoing.m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 7B30D45DE50 for ; Wed, 16 Jun 2010 09:22:25 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (s6.gw.fujitsu.co.jp [10.0.50.96]) by m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 5F0B745DE4F for ; Wed, 16 Jun 2010 09:22:25 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id 3DE46E38002 for ; Wed, 16 Jun 2010 09:22:25 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id DB2901DB8012 for ; Wed, 16 Jun 2010 09:22:24 +0900 (JST) Date: Wed, 16 Jun 2010 09:17:55 +0900 From: KAMEZAWA Hiroyuki 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org 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 List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org