From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id CBB2E6B0038 for ; Tue, 4 Oct 2016 16:32:38 -0400 (EDT) Received: by mail-io0-f198.google.com with SMTP id s30so125214981ioi.0 for ; Tue, 04 Oct 2016 13:32:38 -0700 (PDT) Received: from ipmail07.adl2.internode.on.net (ipmail07.adl2.internode.on.net. [150.101.137.131]) by mx.google.com with ESMTP id l30si7693534iod.131.2016.10.04.13.32.37 for ; Tue, 04 Oct 2016 13:32:38 -0700 (PDT) Date: Wed, 5 Oct 2016 07:32:02 +1100 From: Dave Chinner Subject: Re: [RFC PATCH] mm, compaction: allow compaction for GFP_NOFS requests Message-ID: <20161004203202.GY9806@dastard> References: <20161004081215.5563-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161004081215.5563-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Mel Gorman , Vlastimil Babka , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, LKML , Michal Hocko On Tue, Oct 04, 2016 at 10:12:15AM +0200, Michal Hocko wrote: > From: Michal Hocko > > compaction has been disabled for GFP_NOFS and GFP_NOIO requests since > the direct compaction was introduced by 56de7263fcf3 ("mm: compaction: > direct compact when a high-order allocation fails"). The main reason > is that the migration of page cache pages might recurse back to fs/io > layer and we could potentially deadlock. This is overly conservative > because all the anonymous memory is migrateable in the GFP_NOFS context > just fine. This might be a large portion of the memory in many/most > workkloads. > > Remove the GFP_NOFS restriction and make sure that we skip all fs pages > (those with a mapping) while isolating pages to be migrated. We cannot > consider clean fs pages because they might need a metadata update so > only isolate pages without any mapping for nofs requests. > > The effect of this patch will be probably very limited in many/most > workloads because higher order GFP_NOFS requests are quite rare, You say they are rare only because you don't know how to trigger them easily. :/ Try this: # mkfs.xfs -f -n size=64k # mount /mnt/scratch # time ./fs_mark -D 10000 -S0 -n 100000 -s 0 -L 32 \ -d /mnt/scratch/0 -d /mnt/scratch/1 \ -d /mnt/scratch/2 -d /mnt/scratch/3 \ -d /mnt/scratch/4 -d /mnt/scratch/5 \ -d /mnt/scratch/6 -d /mnt/scratch/7 \ -d /mnt/scratch/8 -d /mnt/scratch/9 \ -d /mnt/scratch/10 -d /mnt/scratch/11 \ -d /mnt/scratch/12 -d /mnt/scratch/13 \ -d /mnt/scratch/14 -d /mnt/scratch/15 As soon as tail pushing on the journal starts (a few seconds in, most likely), you'll start to see lots of 65kB allocations being requested in GFP_NOFS context by the xfs-cil-worker context doing journal checkpoint formatting.... Cheers, Dave. -- Dave Chinner david@fromorbit.com -- 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