From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 1DFE06B0033 for ; Wed, 25 Jan 2017 05:19:53 -0500 (EST) Received: by mail-wm0-f72.google.com with SMTP id t18so35976180wmt.7 for ; Wed, 25 Jan 2017 02:19:53 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id g9si20614496wmc.77.2017.01.25.02.19.51 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 25 Jan 2017 02:19:52 -0800 (PST) Date: Wed, 25 Jan 2017 11:19:47 +0100 From: Michal Hocko Subject: Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically Message-ID: <20170125101947.GH32377@dhcp22.suse.cz> References: <20161220134904.21023-1-mhocko@kernel.org> <20161220134904.21023-3-mhocko@kernel.org> <001f01d272f7$e53acbd0$afb06370$@alibaba-inc.com> <20170124124048.GE6867@dhcp22.suse.cz> <003a01d276d8$c41e0180$4c5a0480$@alibaba-inc.com> <20170125075956.GA32377@dhcp22.suse.cz> <004101d276e6$e1e829d0$a5b87d70$@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <004101d276e6$e1e829d0$a5b87d70$@alibaba-inc.com> Sender: owner-linux-mm@kvack.org List-ID: To: Hillf Danton Cc: 'Andrew Morton' , 'Johannes Weiner' , 'Tetsuo Handa' , 'David Rientjes' , 'Mel Gorman' , linux-mm@kvack.org, 'LKML' On Wed 25-01-17 16:41:54, Hillf Danton wrote: > On Wednesday, January 25, 2017 4:00 PM Michal Hocko wrote: > > On Wed 25-01-17 15:00:51, Hillf Danton wrote: > > > On Tuesday, January 24, 2017 8:41 PM Michal Hocko wrote: > > > > On Fri 20-01-17 16:33:36, Hillf Danton wrote: > > > > > > > > > > On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote: > > > > > > > > > > > > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc) > > > > > > * make sure exclude 0 mask - all other users should have at least > > > > > > * ___GFP_DIRECT_RECLAIM to get here. > > > > > > */ > > > > > > - if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL))) > > > > > > + if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS)) > > > > > > return true; > > > > > > > > > > > As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask > > > > > one bit after another? > > > > > > > > > > if (oc->gfp_mask) { > > > > > if (!(oc->gfp_mask & __GFP_FS)) > > > > > return false; > > > > > > > > > > /* No service for request that can handle fail result itself */ > > > > > if (!(oc->gfp_mask & __GFP_NOFAIL)) > > > > > return false; > > > > > } > > > > > > > > I really do not understand this request. > > > > > > It's a request of both NOFS and NOFAIL, and I think we can keep it from > > > hitting oom killer by shuffling the current gfp checks. > > > I hope it can make nit sense to your work. > > > > > > > I still do not understand. The whole point we are doing the late > > __GFP_FS check is explained in 3da88fb3bacf ("mm, oom: move GFP_NOFS > > check to out_of_memory"). And the reason why I am _removing_ > > __GFP_NOFAIL is explained in the changelog of this patch. > > > > > > This patch is removing the __GFP_NOFAIL part... > > > > > > Yes, and I don't stick to handling NOFAIL requests inside oom. > > > > > > > Besides that why should they return false? > > > > > > It's feedback to page allocator that no kill is issued, and > > > extra attention is needed. > > > > Be careful, the semantic of out_of_memory is different. Returning false > > means that the oom killer has been disabled and so the allocation should > > fail rather than loop for ever. > > > By returning false, I mean that oom killer is making no progress. > And I prefer to give up looping if oom killer can't help. > It's a change in the current semantic to fail the request and I have > to test it isn't bad. And it is really off-topic to this particular patch which really confused me. And no, this wouldn't fly. I have tried that 2 years ago and failed because the risk of unexpected ENOMEM is just too high. -- 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