From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 00E766B0033 for ; Wed, 25 Oct 2017 08:41:54 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id g75so20855113pfg.4 for ; Wed, 25 Oct 2017 05:41:53 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id u21si1922623pfl.480.2017.10.25.05.41.52 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 25 Oct 2017 05:41:52 -0700 (PDT) Date: Wed, 25 Oct 2017 14:41:47 +0200 From: Michal Hocko Subject: Re: [RFC PATCH 2/2] mm,oom: Try last second allocation after selecting an OOM victim. Message-ID: <20171025124147.bvd4huwtykf6icmb@dhcp22.suse.cz> References: <20171023113057.bdfte7ihtklhjbdy@dhcp22.suse.cz> <201710242024.EDH13579.VQLFtFFMOOHSOJ@I-love.SAKURA.ne.jp> <20171024114104.twg73jvyjevovkjm@dhcp22.suse.cz> <201710251948.EJH00500.MOOStFLFQOHFJV@I-love.SAKURA.ne.jp> <20171025110955.jsc4lqjbg6ww5va6@dhcp22.suse.cz> <201710252115.JII86453.tFFSLHQOOOVMJF@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201710252115.JII86453.tFFSLHQOOOVMJF@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: hannes@cmpxchg.org, aarcange@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, mgorman@suse.de, oleg@redhat.com, vdavydov.dev@gmail.com, vbabka@suse.cz On Wed 25-10-17 21:15:24, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Wed 25-10-17 19:48:09, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > [...] > > > > The OOM killer is the last hand break. At the time you hit the OOM > > > > condition your system is usually hard to use anyway. And that is why I > > > > do care to make this path deadlock free. I have mentioned multiple times > > > > that I find real life triggers much more important than artificial DoS > > > > like workloads which make your system unsuable long before you hit OOM > > > > killer. > > > > > > Unable to invoke the OOM killer (i.e. OOM lockup) is worse than hand break injury. > > > > > > If you do care to make this path deadlock free, you had better stop depending on > > > mutex_trylock(&oom_lock). Not only printk() from oom_kill_process() can trigger > > > deadlock due to console_sem versus oom_lock dependency but also > > > > And this means that we have to fix printk. Completely silent oom path is > > out of question IMHO > > We cannot fix printk() without giving enough CPU resource to printk(). This is a separate discussion but having a basically unbound time spent in printk is simply a no-go. > I don't think "Completely silent oom path" can happen, for warn_alloc() is called > again when it is retried. But anyway, let's remove warn_alloc(). I mean something else. We simply cannot do the oom killing without telling userspace about that. And printk is the only API we can use for that. -- 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