From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752433AbcGUMNX (ORCPT ); Thu, 21 Jul 2016 08:13:23 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:53850 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751892AbcGUMNT (ORCPT ); Thu, 21 Jul 2016 08:13:19 -0400 Date: Thu, 21 Jul 2016 08:13:00 -0400 From: Johannes Weiner To: Michal Hocko Cc: David Rientjes , linux-mm@kvack.org, Mikulas Patocka , Ondrej Kozina , Tetsuo Handa , Mel Gorman , Neil Brown , Andrew Morton , LKML , dm-devel@redhat.com Subject: Re: [RFC PATCH 1/2] mempool: do not consume memory reserves from the reclaim path Message-ID: <20160721121300.GA21806@cmpxchg.org> References: <1468831164-26621-1-git-send-email-mhocko@kernel.org> <1468831285-27242-1-git-send-email-mhocko@kernel.org> <20160719135426.GA31229@cmpxchg.org> <20160720081541.GF11249@dhcp22.suse.cz> <20160721085202.GC26379@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160721085202.GC26379@dhcp22.suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 21, 2016 at 10:52:03AM +0200, Michal Hocko wrote: > Look, there are > $ git grep mempool_alloc | wc -l > 304 > > many users of this API and we do not want to flip the default behavior > which is there for more than 10 years. So far you have been arguing > about potential deadlocks and haven't shown any particular path which > would have a direct or indirect dependency between mempool and normal > allocator and it wouldn't be a bug. As the matter of fact the change > we are discussing here causes a regression. If you want to change the > semantic of mempool allocator then you are absolutely free to do so. In > a separate patch which would be discussed with IO people and other > users, though. But we _absolutely_ want to fix the regression first > and have a simple fix for 4.6 and 4.7 backports. At this moment there > are revert and patch 1 on the table. The later one should make your > backtrace happy and should be only as a temporal fix until we find out > what is actually misbehaving on your systems. If you are not interested > to pursue that way I will simply go with the revert. +1 It's very unlikely that decade-old mempool semantics are suddenly a fundamental livelock problem, when all the evidence we have is one hang and vague speculation. Given that the patch causes regressions, and that the bug is most likely elsewhere anyway, a full revert rather than merely-less-invasive mempool changes makes the most sense to me. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 22F8682963 for ; Thu, 21 Jul 2016 08:13:12 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id o80so12003978wme.1 for ; Thu, 21 Jul 2016 05:13:12 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id e73si4070970lji.68.2016.07.21.05.13.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 Jul 2016 05:13:10 -0700 (PDT) Date: Thu, 21 Jul 2016 08:13:00 -0400 From: Johannes Weiner Subject: Re: [RFC PATCH 1/2] mempool: do not consume memory reserves from the reclaim path Message-ID: <20160721121300.GA21806@cmpxchg.org> References: <1468831164-26621-1-git-send-email-mhocko@kernel.org> <1468831285-27242-1-git-send-email-mhocko@kernel.org> <20160719135426.GA31229@cmpxchg.org> <20160720081541.GF11249@dhcp22.suse.cz> <20160721085202.GC26379@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160721085202.GC26379@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: David Rientjes , linux-mm@kvack.org, Mikulas Patocka , Ondrej Kozina , Tetsuo Handa , Mel Gorman , Neil Brown , Andrew Morton , LKML , dm-devel@redhat.com On Thu, Jul 21, 2016 at 10:52:03AM +0200, Michal Hocko wrote: > Look, there are > $ git grep mempool_alloc | wc -l > 304 > > many users of this API and we do not want to flip the default behavior > which is there for more than 10 years. So far you have been arguing > about potential deadlocks and haven't shown any particular path which > would have a direct or indirect dependency between mempool and normal > allocator and it wouldn't be a bug. As the matter of fact the change > we are discussing here causes a regression. If you want to change the > semantic of mempool allocator then you are absolutely free to do so. In > a separate patch which would be discussed with IO people and other > users, though. But we _absolutely_ want to fix the regression first > and have a simple fix for 4.6 and 4.7 backports. At this moment there > are revert and patch 1 on the table. The later one should make your > backtrace happy and should be only as a temporal fix until we find out > what is actually misbehaving on your systems. If you are not interested > to pursue that way I will simply go with the revert. +1 It's very unlikely that decade-old mempool semantics are suddenly a fundamental livelock problem, when all the evidence we have is one hang and vague speculation. Given that the patch causes regressions, and that the bug is most likely elsewhere anyway, a full revert rather than merely-less-invasive mempool changes makes the most sense to me. -- 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