From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933172AbcDKNn2 (ORCPT ); Mon, 11 Apr 2016 09:43:28 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:35712 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932516AbcDKNnY (ORCPT ); Mon, 11 Apr 2016 09:43:24 -0400 Date: Mon, 11 Apr 2016 15:43:21 +0200 From: Michal Hocko To: Tetsuo Handa Cc: linux-mm@kvack.org, rientjes@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, oleg@redhat.com Subject: Re: [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skip regular OOM killer path Message-ID: <20160411134321.GI23157@dhcp22.suse.cz> References: <201604072038.CHC51027.MSJOFVLHOFFtQO@I-love.SAKURA.ne.jp> <201604082019.EDH52671.OJHQFMStOFLVOF@I-love.SAKURA.ne.jp> <20160408115033.GH29820@dhcp22.suse.cz> <201604091339.FAJ12491.FVHQFFMSJLtOOO@I-love.SAKURA.ne.jp> <20160411120238.GF23157@dhcp22.suse.cz> <201604112226.IFC52662.FOFVtQSJLOFMOH@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201604112226.IFC52662.FOFVtQSJLOFMOH@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 11-04-16 22:26:09, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Sat 09-04-16 13:39:30, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > On Fri 08-04-16 20:19:28, Tetsuo Handa wrote: > > > > > I looked at next-20160408 but I again came to think that we should remove > > > > > these shortcuts (something like a patch shown bottom). > > > > > > > > feel free to send the patch with the full description. But I would > > > > really encourage you to check the history to learn why those have been > > > > added and describe why those concerns are not valid/important anymore. > > > > > > I believe that past discussions and decisions about current code are too > > > optimistic because they did not take 'The "too small to fail" memory- > > > allocation rule' problem into account. > > > > In most cases they were driven by _real_ usecases though. And that > > is what matters. Theoretically possible issues which happen under > > crazy workloads which are DoSing the machine already are not something > > to optimize for. Sure we should try to cope with them as gracefully > > as possible, no questions about that, but we should try hard not to > > reintroduce previous issues during _sensible_ workloads. > > I'm not requesting you to optimize for crazy workloads. None of my > customers intentionally put crazy workloads, but they are getting silent > hangups and I'm suspecting that something went wrong with memory management. There are many other possible reasons for thses symptoms. Have you actually seen any _evidence_ they the hang they are seeing is due to oom deadlock, though. A single crash dump or consistent sysrq output which would point that direction. > But there is no evidence because memory management subsystem remains silent. > You call my testcases DoS, but there is no evidence that my customers > are not hitting the same problem my testcases found. This is really impossible to comment on. > I'm suggesting you to at least emit diagnostic messages when something went > wrong. That is what kmallocwd is for. And if you do not want to emit > diagnostic messages, I'm fine with timeout based approach. I am all for more diagnostic but what you were proposing was so heavy weight it doesn't really seem worth it. Anyway yet again this is getting largely off-topic... -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by kanga.kvack.org (Postfix) with ESMTP id 1720D6B025F for ; Mon, 11 Apr 2016 09:43:24 -0400 (EDT) Received: by mail-wm0-f53.google.com with SMTP id v188so87029143wme.1 for ; Mon, 11 Apr 2016 06:43:24 -0700 (PDT) Received: from mail-wm0-f66.google.com (mail-wm0-f66.google.com. [74.125.82.66]) by mx.google.com with ESMTPS id 129si13594952wms.67.2016.04.11.06.43.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Apr 2016 06:43:23 -0700 (PDT) Received: by mail-wm0-f66.google.com with SMTP id n3so21427143wmn.1 for ; Mon, 11 Apr 2016 06:43:22 -0700 (PDT) Date: Mon, 11 Apr 2016 15:43:21 +0200 From: Michal Hocko Subject: Re: [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skip regular OOM killer path Message-ID: <20160411134321.GI23157@dhcp22.suse.cz> References: <201604072038.CHC51027.MSJOFVLHOFFtQO@I-love.SAKURA.ne.jp> <201604082019.EDH52671.OJHQFMStOFLVOF@I-love.SAKURA.ne.jp> <20160408115033.GH29820@dhcp22.suse.cz> <201604091339.FAJ12491.FVHQFFMSJLtOOO@I-love.SAKURA.ne.jp> <20160411120238.GF23157@dhcp22.suse.cz> <201604112226.IFC52662.FOFVtQSJLOFMOH@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201604112226.IFC52662.FOFVtQSJLOFMOH@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: linux-mm@kvack.org, rientjes@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, oleg@redhat.com On Mon 11-04-16 22:26:09, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Sat 09-04-16 13:39:30, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > On Fri 08-04-16 20:19:28, Tetsuo Handa wrote: > > > > > I looked at next-20160408 but I again came to think that we should remove > > > > > these shortcuts (something like a patch shown bottom). > > > > > > > > feel free to send the patch with the full description. But I would > > > > really encourage you to check the history to learn why those have been > > > > added and describe why those concerns are not valid/important anymore. > > > > > > I believe that past discussions and decisions about current code are too > > > optimistic because they did not take 'The "too small to fail" memory- > > > allocation rule' problem into account. > > > > In most cases they were driven by _real_ usecases though. And that > > is what matters. Theoretically possible issues which happen under > > crazy workloads which are DoSing the machine already are not something > > to optimize for. Sure we should try to cope with them as gracefully > > as possible, no questions about that, but we should try hard not to > > reintroduce previous issues during _sensible_ workloads. > > I'm not requesting you to optimize for crazy workloads. None of my > customers intentionally put crazy workloads, but they are getting silent > hangups and I'm suspecting that something went wrong with memory management. There are many other possible reasons for thses symptoms. Have you actually seen any _evidence_ they the hang they are seeing is due to oom deadlock, though. A single crash dump or consistent sysrq output which would point that direction. > But there is no evidence because memory management subsystem remains silent. > You call my testcases DoS, but there is no evidence that my customers > are not hitting the same problem my testcases found. This is really impossible to comment on. > I'm suggesting you to at least emit diagnostic messages when something went > wrong. That is what kmallocwd is for. And if you do not want to emit > diagnostic messages, I'm fine with timeout based approach. I am all for more diagnostic but what you were proposing was so heavy weight it doesn't really seem worth it. Anyway yet again this is getting largely off-topic... -- 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