From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757847Ab0FOOQV (ORCPT ); Tue, 15 Jun 2010 10:16:21 -0400 Received: from gir.skynet.ie ([193.1.99.77]:50668 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753266Ab0FOOQU (ORCPT ); Tue, 15 Jun 2010 10:16:20 -0400 Date: Tue, 15 Jun 2010 15:16:01 +0100 From: Mel Gorman To: Rik van Riel Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Chris Mason , Nick Piggin , Johannes Weiner , Christoph Hellwig , KAMEZAWA Hiroyuki , Andrew Morton Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <4C178868.2010002@redhat.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mel Gorman Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim Date: Tue, 15 Jun 2010 15:16:01 +0100 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Chris Mason , Nick Piggin , Johannes Weiner , Christoph Hellwig , KAMEZAWA Hiroyuki , Andrew Morton To: Rik van Riel Return-path: Content-Disposition: inline In-Reply-To: <4C178868.2010002@redhat.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org 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. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/ . 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