From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760209AbcBYJIq (ORCPT ); Thu, 25 Feb 2016 04:08:46 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:36295 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759156AbcBYJIm (ORCPT ); Thu, 25 Feb 2016 04:08:42 -0500 Date: Thu, 25 Feb 2016 10:08:39 +0100 From: Michal Hocko To: Nikolay Borisov Cc: Konstantin Khlebnikov , "Theodore Ts'o" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dmitry Monakhov , Johannes Weiner , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org Subject: Re: [PATCH RFC] ext4: use __GFP_NOFAIL in ext4_free_blocks() Message-ID: <20160225090839.GC17573@dhcp22.suse.cz> References: <20160224170912.2195.8153.stgit@buzz> <56CEC2EC.5000506@kyup.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56CEC2EC.5000506@kyup.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 25-02-16 11:01:32, Nikolay Borisov wrote: > > > On 02/24/2016 07:09 PM, Konstantin Khlebnikov wrote: > > This might be unexpected but pages allocated for sbi->s_buddy_cache are > > charged to current memory cgroup. So, GFP_NOFS allocation could fail if > > current task has been killed by OOM or if current memory cgroup has no > > free memory left. Block allocator cannot handle such failures here yet. > > > > Signed-off-by: Konstantin Khlebnikov > > Adding new users of GFP_NOFAIL is deprecated. This is not true. GFP_NOFAIL should be used where the allocation failure is no tolleratable and it is much more preferrable to doing an opencoded endless loop over page allocator. > Where exactly does the > block allocator fail, I skimmed the code and failing ext4_mb_load_buddy > seems to be handled at all call sites. There are some BUG_ONs but from > the comments there I guess they should occur when we try to find a page > and not allocate a new one? I have posted a similar patch last year: http://lkml.kernel.org/r/1438768284-30927-6-git-send-email-mhocko@kernel.org because I could see emergency reboots when GFP_NOFS allocations were allowed to fail. -- Michal Hocko SUSE Labs