From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx148.postini.com [74.125.245.148]) by kanga.kvack.org (Postfix) with SMTP id B45476B0037 for ; Mon, 17 Jun 2013 14:15:36 -0400 (EDT) Message-ID: <51BF519C.9000508@redhat.com> Date: Mon, 17 Jun 2013 14:12:44 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 1/7] mm: remove ZONE_RECLAIM_LOCKED References: <1370445037-24144-1-git-send-email-aarcange@redhat.com> <1370445037-24144-2-git-send-email-aarcange@redhat.com> <20130606090430.GC1936@suse.de> <51B0C8D8.7070708@redhat.com> <51BB41EF.7080508@redhat.com> <20130617093010.GH1875@suse.de> In-Reply-To: <20130617093010.GH1875@suse.de> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrea Arcangeli , linux-mm@kvack.org, Hugh Dickins , Richard Davies , Shaohua Li , Rafael Aquini On 06/17/2013 05:30 AM, Mel Gorman wrote: > On Fri, Jun 14, 2013 at 12:16:47PM -0400, Rik van Riel wrote: >> On 06/06/2013 01:37 PM, Rik van Riel wrote: >>> On 06/06/2013 05:04 AM, Mel Gorman wrote: >>>> On Wed, Jun 05, 2013 at 05:10:31PM +0200, Andrea Arcangeli wrote: >>>>> Zone reclaim locked breaks zone_reclaim_mode=1. If more than one >>>>> thread allocates memory at the same time, it forces a premature >>>>> allocation into remote NUMA nodes even when there's plenty of clean >>>>> cache to reclaim in the local nodes. >>>>> >>>>> Signed-off-by: Andrea Arcangeli >>>> >>>> Be aware that after this patch is applied that it is possible to have a >>>> situation like this >>>> >>>> 1. 4 processes running on node 1 >>>> 2. Each process tries to allocate 30% of memory >>>> 3. Each process reads the full buffer in a loop (stupid, just an example) >>>> >>>> In this situation the processes will continually interfere with each >>>> other until one of them gets migrated to another zone by the scheduler. >>> >>> This is a very good point. >>> >>> Andrea, I suspect we will need some kind of safeguard against >>> this problem. >> >> Never mind me. >> >> In __zone_reclaim we set the flags in swap_control so >> we never unmap pages or swap pages out at all by >> default, so this should not be an issue at all. >> >> In order to get the problem illustrated above, the >> user will have to enable RECLAIM_SWAP through sysfs >> manually. >> > > For the mapped case and the default tuning for zone_reclaim_mode then > yes. If instead of allocating 30% of memory the processes are using using > buffered reads/writes then they'll reach each others page cache pages and > it's a very similar problem. Could we fix that problem by simply allowing page cache allocations (__GFP_WRITE) to fall back to other zones, regardless of the zone_reclaim setting? The ZONE_RECLAIM_LOCKED function seems to break as many things as it fixes, so replacing it with something else seems like a worthwhile pursuit... -- 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