From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id C009F6B0038 for ; Wed, 5 Oct 2016 07:38:48 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id l138so155008802wmg.3 for ; Wed, 05 Oct 2016 04:38:48 -0700 (PDT) Received: from mail-wm0-f66.google.com (mail-wm0-f66.google.com. [74.125.82.66]) by mx.google.com with ESMTPS id io8si10598047wjb.284.2016.10.05.04.38.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Oct 2016 04:38:47 -0700 (PDT) Received: by mail-wm0-f66.google.com with SMTP id p138so24124881wmb.0 for ; Wed, 05 Oct 2016 04:38:47 -0700 (PDT) Date: Wed, 5 Oct 2016 13:38:45 +0200 From: Michal Hocko Subject: Re: [RFC PATCH] mm, compaction: allow compaction for GFP_NOFS requests Message-ID: <20161005113839.GC7138@dhcp22.suse.cz> References: <20161004081215.5563-1-mhocko@kernel.org> <20161004203202.GY9806@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161004203202.GY9806@dastard> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Chinner Cc: Mel Gorman , Vlastimil Babka , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, LKML On Wed 05-10-16 07:32:02, Dave Chinner wrote: > 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. :/ true > 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 Does this simulate a standard or usual fs workload/configuration? I am not questioning that higher order NOFS allocations are non-existent - that's why I came with the patch in the first place ;). My observation was that they are so rare that the visible effect of this patch might be quite low or even hard to notice. Anyway, thanks for a _useful_ testcase to play with! Let's see what numbers I get from this. -- Michal Hocko SUSE Labs -- 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