From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751405AbdAYImW (ORCPT ); Wed, 25 Jan 2017 03:42:22 -0500 Received: from out0-154.mail.aliyun.com ([140.205.0.154]:54247 "EHLO out0-154.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751260AbdAYImV (ORCPT ); Wed, 25 Jan 2017 03:42:21 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R821e4;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e02c03291;MF=hillf.zj@alibaba-inc.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---.7W2yWYw_1485333714; Reply-To: "Hillf Danton" From: "Hillf Danton" To: "'Michal Hocko'" Cc: "'Andrew Morton'" , "'Johannes Weiner'" , "'Tetsuo Handa'" , "'David Rientjes'" , "'Mel Gorman'" , , "'LKML'" 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> In-Reply-To: <20170125075956.GA32377@dhcp22.suse.cz> Subject: Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically Date: Wed, 25 Jan 2017 16:41:54 +0800 Message-ID: <004101d276e6$e1e829d0$a5b87d70$@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQI5GhCbBXj+0AWvuNrZg+/tQ4jXjAKoT3afAkvunb0BwIhoHAIPpCOcAcoJgdGgJx/DIA== Content-Language: zh-cn Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. thanks Hillf