From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 6C5226B0232 for ; Tue, 15 Jun 2010 09:59:48 -0400 (EDT) Date: Tue, 15 Jun 2010 14:59:28 +0100 From: Mel Gorman Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim Message-ID: <20100615135928.GK26788@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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <4C17815A.8080402@redhat.com> Sender: owner-linux-mm@kvack.org 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 List-ID: On Tue, Jun 15, 2010 at 09:34:18AM -0400, Rik van Riel wrote: > On 06/15/2010 07:45 AM, Mel Gorman wrote: >> On Mon, Jun 14, 2010 at 05:55:51PM -0400, Rik van Riel wrote: >>> On 06/14/2010 07:17 AM, Mel Gorman wrote: >>> >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index 4856a2a..574e816 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>>> @@ -372,6 +372,12 @@ int write_reclaim_page(struct page *page, struct address_space *mapping, >>>> return PAGE_SUCCESS; >>>> } >>>> >>>> +/* 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; >>>> +} >>>> + >>> >>> I'm not entirely convinced on this bit, but am willing to >>> be convinced by the data. >>> >> >> Which bit? >> >> You're not convinced that kswapd should be allowed to write back? >> You're not convinced that memcg should be allowed to write back? >> You're not convinced that direct reclaim writing back pages can overflow >> the stack? > > 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? -- 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/ . Don't email: email@kvack.org