From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f171.google.com (mail-ob0-f171.google.com [209.85.214.171]) by kanga.kvack.org (Postfix) with ESMTP id 10C066B0005 for ; Fri, 19 Feb 2016 09:37:11 -0500 (EST) Received: by mail-ob0-f171.google.com with SMTP id gc3so107662397obb.3 for ; Fri, 19 Feb 2016 06:37:11 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id w128si17033471oie.5.2016.02.19.06.37.09 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 19 Feb 2016 06:37:10 -0800 (PST) Subject: Re: [PATCH] mm: memcontrol: Pass NULL memcg for oom_badness() check. From: Tetsuo Handa References: <1455889898-5659-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20160219140406.GF12690@dhcp22.suse.cz> In-Reply-To: <20160219140406.GF12690@dhcp22.suse.cz> Message-Id: <201602192336.EJF90671.HMFLFSVOFJOtOQ@I-love.SAKURA.ne.jp> Date: Fri, 19 Feb 2016 23:36:55 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org Cc: rientjes@google.com, hannes@cmpxchg.org, vdavydov@virtuozzo.com, linux-mm@kvack.org Michal Hocko wrote: > On Fri 19-02-16 22:51:38, Tetsuo Handa wrote: > > Currently, mem_cgroup_out_of_memory() is calling > > oom_scan_process_thread(&oc, task, totalpages) which includes > > a call to oom_unkillable_task(task, NULL, NULL) and then is > > calling oom_badness(task, memcg, NULL, totalpages) which includes > > a call to oom_unkillable_task(task, memcg, NULL). > > > > Since for_each_mem_cgroup_tree() iterates on only tasks from the given > > memcg hierarchy, there is no point with passing non-NULL memcg argument > > to oom_unkillable_task() via oom_badness(). > > > > Replace memcg argument with NULL in order to save a call to > > task_in_mem_cgroup(task, memcg) in oom_unkillable_task() > > which is always true. > > yes this is true but oom_badness is called from super slow path here so > I am not sure this change will buy anything. It makes the code little > bit more confusing because now you have to think twice (or git blame) to > see why the memcg == NULL is really OK. > > So I do not think this is an improvement. If anything wouldn't it be > cleaner to remove memcg parameter from oom_badness altogether and > instead do the task_in_mem_cgroup check where it is really needed? > In other words do the check in oom_kill_process when evaluating children > to sacrifice them? This patch is a clarification before proposing http://lkml.kernel.org/r/1455892411-7611-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp which converts two oom_unkillable_task() calls into one and fixes infinite loop which will occur after we merge the OOM reaper. -- 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