From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751819AbdCOIfh (ORCPT ); Wed, 15 Mar 2017 04:35:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:54972 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751416AbdCOIfd (ORCPT ); Wed, 15 Mar 2017 04:35:33 -0400 Date: Wed, 15 Mar 2017 09:35:29 +0100 From: Michal Hocko To: "Luis R. Rodriguez" Cc: "Darrick J. Wong" , Brian Foster , Christoph Hellwig , Tetsuo Handa , Xiong Zhou , linux-xfs@vger.kernel.org, linux-mm@kvack.org, LKML , linux-fsdevel@vger.kernel.org, Dave Chinner , sebastian.parschauer@suse.com, AlNovak@suse.com, jack@suse.cz, Greg Kroah-Hartman Subject: Re: [PATCH v2] xfs: remove kmem_zalloc_greedy Message-ID: <20170315083529.GD32620@dhcp22.suse.cz> References: <20170308003528.GK5280@birch.djwong.org> <20170314165745.GB28800@wotan.suse.de> <20170314180738.GV5280@birch.djwong.org> <20170315001427.GI28800@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170315001427.GI28800@wotan.suse.de> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 15-03-17 01:14:27, Luis R. Rodriguez wrote: > On Tue, Mar 14, 2017 at 11:07:38AM -0700, Darrick J. Wong wrote: > > On Tue, Mar 14, 2017 at 05:57:45PM +0100, Luis R. Rodriguez wrote: > > > On Tue, Mar 07, 2017 at 04:35:28PM -0800, Darrick J. Wong wrote: > > > > The sole remaining caller of kmem_zalloc_greedy is bulkstat, which uses > > > > it to grab 1-4 pages for staging of inobt records. The infinite loop in > > > > the greedy allocation function is causing hangs[1] in generic/269, so > > > > just get rid of the greedy allocator in favor of kmem_zalloc_large. > > > > This makes bulkstat somewhat more likely to ENOMEM if there's really no > > > > pages to spare, but eliminates a source of hangs. > > > > > > > > [1] http://lkml.kernel.org/r/20170301044634.rgidgdqqiiwsmfpj%40XZHOUW.usersys.redhat.com > > > > > > > > Signed-off-by: Darrick J. Wong > > > > --- > > > > v2: remove single-page fallback > > > > --- > > > > > > Since this fixes a hang how about *at the very least* a respective Fixes tag ? > > > This fixes an existing hang so what are the stable considerations here ? I > > > realize the answer is not easy but figured its worth asking. > > > > I didn't think it was appropriate to "Fixes: 77e4635ae1917" since we're > > not fixing _greedy so much as we are killing it. The patch fixes an > > infinite retry hang when bulkstat tries a memory allocation that cannot > > be satisfied; and having done that, realizes there are no remaining > > callers of _greedy and garbage collects it. The code that was there > > before also seems capable of sleeping forever, I think. > > > > So the minimally invasive fix is to apply the allocation conversion in > > bulkstat, and if there aren't any other callers of _greedy then you can > > get rid of it too. > > For the stake of stable XFS users then why not do the less invasive change > first, Cc stable, and then move on to the less backward portable solution ? The thing is that the permanent failures for vmalloc were so unlikely prior to 5d17a73a2ebe ("vmalloc: back off when the current task is killed") that this was basically a non-issue before this (4.11) merge window. -- Michal Hocko SUSE Labs