From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id B08706B0003 for ; Tue, 29 May 2018 13:28:19 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id f5-v6so4177730pgq.19 for ; Tue, 29 May 2018 10:28:19 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id m64-v6si33067758pfm.0.2018.05.29.10.28.18 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 29 May 2018 10:28:18 -0700 (PDT) Date: Tue, 29 May 2018 19:28:15 +0200 From: Michal Hocko Subject: Re: [PATCH] mm,oom: Don't call schedule_timeout_killable() with oom_lock held. Message-ID: <20180529172815.GY27180@dhcp22.suse.cz> References: <20180515091655.GD12670@dhcp22.suse.cz> <201805181914.IFF18202.FOJOVSOtLFMFHQ@I-love.SAKURA.ne.jp> <20180518122045.GG21711@dhcp22.suse.cz> <201805210056.IEC51073.VSFFHFOOQtJMOL@I-love.SAKURA.ne.jp> <20180522061850.GB20020@dhcp22.suse.cz> <201805231924.EED86916.FSQJMtHOLVOFOF@I-love.SAKURA.ne.jp> <20180529071736.GI27180@dhcp22.suse.cz> <20180529081639.GM27180@dhcp22.suse.cz> <40a5a42f-6812-b4ee-a72e-7f01dc9de464@i-love.sakura.ne.jp> <20180529171833.GX27180@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180529171833.GX27180@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: guro@fb.com, rientjes@google.com, hannes@cmpxchg.org, vdavydov.dev@gmail.com, tj@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, torvalds@linux-foundation.org On Tue 29-05-18 19:18:33, Michal Hocko wrote: > On Tue 29-05-18 23:33:13, Tetsuo Handa wrote: > > On 2018/05/29 17:16, Michal Hocko wrote: > > > With the full changelog. This can be either folded into the respective > > > patch or applied on top. > > > > > >>From 0bd619e7a68337c97bdaed288e813e96a14ba339 Mon Sep 17 00:00:00 2001 > > > From: Michal Hocko > > > Date: Tue, 29 May 2018 10:09:33 +0200 > > > Subject: [PATCH] mm, memcg, oom: fix pre-mature allocation failures > > > > > > Tetsuo has noticed that "mm, oom: cgroup-aware OOM killer" can lead to a > > > pre-mature allocation failure if the cgroup aware oom killer is enabled > > > and select_victim_memcg doesn't pick up any memcg to kill because there > > > is a memcg already being killed. oc->chosen_memcg will become INFLIGHT_VICTIM > > > and oom_kill_memcg_victim will bail out early. oc->chosen_task will > > > stay NULL, however, and out_of_memory will therefore return false which > > > forces __alloc_pages_may_oom to not set did_some_progress and the page > > > allocator backs out and fails the allocation. > > > U > > > Fix this by checking both chosen_task and chosen_memcg in out_of_memory > > > and return false only when _both_ are NULL. > > > > I don't like this patch. It is not easy to understand and is fragile to > > future changes. Currently the only case !!oc->chosen can become false is that > > there was no eligible tasks when SysRq-f was requested or memcg OOM occurred. > > Well, the current contract is not easy unfortunatelly. We have two > different modes of operation. We are either killing whole cgroups or a > task from a cgroup. In any case, the contract says that if we have any > killable entity then at least one of chosen* is set to INFLIGHT_VICTIM. > Other than that one of them has to be !NULL or we have no eligible > killable entity. The return value reflects all these cases. Btw. if your concern is the readability then we can add a helper and decsribe all the above in the comment. -- Michal Hocko SUSE Labs