From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754230AbcJDUcj (ORCPT ); Tue, 4 Oct 2016 16:32:39 -0400 Received: from ipmail07.adl2.internode.on.net ([150.101.137.131]:27149 "EHLO ipmail07.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754098AbcJDUci (ORCPT ); Tue, 4 Oct 2016 16:32:38 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2CzKgBfEfRXEJqYLHlcHAEBBAEBCgEBgz0BAQEBAR6BU4J5g3mcFgEBAQEBAQaBGot2hiGEFoYYAgIBAQKBbU0BAgEBAQEBAgYBAQEBAQEBATdAhGEBAQEEOhwjEAgDDgcDCSUPBSUDBxoTiEy/FAEBCAIBJB6FVIUfhCOGAgWZeYkrhj+BeI4ESIZEhWSDfoEUBQeEZyo0hVeCLwEBAQ Date: Wed, 5 Oct 2016 07:32:02 +1100 From: Dave Chinner To: Michal Hocko Cc: Mel Gorman , Vlastimil Babka , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, LKML , Michal Hocko 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> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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