From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754076AbdKILDi (ORCPT ); Thu, 9 Nov 2017 06:03:38 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:27409 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754025AbdKILDf (ORCPT ); Thu, 9 Nov 2017 06:03:35 -0500 To: mhocko@kernel.org Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, xiyou.wangcong@gmail.com, dave.hansen@intel.com, hannes@cmpxchg.org, mgorman@suse.de, pmladek@suse.com, sergey.senozhatsky@gmail.com, vbabka@suse.cz, peterz@infradead.org, torvalds@linux-foundation.org, jack@suse.cz, mathieu.desnoyers@efficios.com, rostedt@rostedt.homelinux.com Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to loadbalance console writes From: Tetsuo Handa References: <20171108102723.602216b1@gandalf.local.home> <20171109101138.qmy3366myzjafexr@dhcp22.suse.cz> <201711091922.IHJ81787.OVQFFJOSOLtHMF@I-love.SAKURA.ne.jp> <20171109102613.hp6waybyxbkb3crz@dhcp22.suse.cz> In-Reply-To: <20171109102613.hp6waybyxbkb3crz@dhcp22.suse.cz> Message-Id: <201711092003.ACJ86411.FOFtFMVOJOSLHQ@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Thu, 9 Nov 2017 20:03:30 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michal Hocko wrote: > On Thu 09-11-17 19:22:58, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > Hi, > > > assuming that this passes warn stall torturing by Tetsuo, do you think > > > we can drop http://lkml.kernel.org/r/1509017339-4802-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp > > > from the mmotm tree? > > > > I don't think so. > > > > The rule that "do not try to printk() faster than the kernel can write to > > consoles" will remain no matter how printk() changes. Unless asynchronous > > approach like https://lwn.net/Articles/723447/ is used, I think we can't > > obtain useful information. > > Does that mean that the patch doesn't pass your test? > Test is irrelevant. See the changelog. Synchronous approach is prone to unexpected results (e.g. too late [1], too frequent [2], overlooked [3]). As far as I know, warn_alloc() never helped with providing information other than "something is going wrong". I want to consider asynchronous approach which can obtain information during stalls with possibly relevant threads (e.g. the owner of oom_lock and kswapd-like threads) and serve as a trigger for actions (e.g. turn on/off tracepoints, ask libvirt daemon to take a memory dump of stalling KVM guest for diagnostic purpose). [1] https://bugzilla.kernel.org/show_bug.cgi?id=192981 [2] http://lkml.kernel.org/r/CAM_iQpWuPVGc2ky8M-9yukECtS+zKjiDasNymX7rMcBjBFyM_A@mail.gmail.com [3] commit db73ee0d46379922 ("mm, vmscan: do not loop on too_many_isolated for ever") From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f70.google.com (mail-it0-f70.google.com [209.85.214.70]) by kanga.kvack.org (Postfix) with ESMTP id B6617440CD7 for ; Thu, 9 Nov 2017 06:04:44 -0500 (EST) Received: by mail-it0-f70.google.com with SMTP id r127so9057681itb.4 for ; Thu, 09 Nov 2017 03:04:44 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [2001:e42:101:1:202:181:97:72]) by mx.google.com with ESMTPS id f25si5780096ioj.105.2017.11.09.03.04.43 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 09 Nov 2017 03:04:43 -0800 (PST) Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to loadbalance console writes From: Tetsuo Handa References: <20171108102723.602216b1@gandalf.local.home> <20171109101138.qmy3366myzjafexr@dhcp22.suse.cz> <201711091922.IHJ81787.OVQFFJOSOLtHMF@I-love.SAKURA.ne.jp> <20171109102613.hp6waybyxbkb3crz@dhcp22.suse.cz> In-Reply-To: <20171109102613.hp6waybyxbkb3crz@dhcp22.suse.cz> Message-Id: <201711092003.ACJ86411.FOFtFMVOJOSLHQ@I-love.SAKURA.ne.jp> Date: Thu, 9 Nov 2017 20:03:30 +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: rostedt@goodmis.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, xiyou.wangcong@gmail.com, dave.hansen@intel.com, hannes@cmpxchg.org, mgorman@suse.de, pmladek@suse.com, sergey.senozhatsky@gmail.com, vbabka@suse.cz, peterz@infradead.org, torvalds@linux-foundation.org, jack@suse.cz, mathieu.desnoyers@efficios.com, rostedt@home.goodmis.org Michal Hocko wrote: > On Thu 09-11-17 19:22:58, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > Hi, > > > assuming that this passes warn stall torturing by Tetsuo, do you think > > > we can drop http://lkml.kernel.org/r/1509017339-4802-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp > > > from the mmotm tree? > > > > I don't think so. > > > > The rule that "do not try to printk() faster than the kernel can write to > > consoles" will remain no matter how printk() changes. Unless asynchronous > > approach like https://lwn.net/Articles/723447/ is used, I think we can't > > obtain useful information. > > Does that mean that the patch doesn't pass your test? > Test is irrelevant. See the changelog. Synchronous approach is prone to unexpected results (e.g. too late [1], too frequent [2], overlooked [3]). As far as I know, warn_alloc() never helped with providing information other than "something is going wrong". I want to consider asynchronous approach which can obtain information during stalls with possibly relevant threads (e.g. the owner of oom_lock and kswapd-like threads) and serve as a trigger for actions (e.g. turn on/off tracepoints, ask libvirt daemon to take a memory dump of stalling KVM guest for diagnostic purpose). [1] https://bugzilla.kernel.org/show_bug.cgi?id=192981 [2] http://lkml.kernel.org/r/CAM_iQpWuPVGc2ky8M-9yukECtS+zKjiDasNymX7rMcBjBFyM_A@mail.gmail.com [3] commit db73ee0d46379922 ("mm, vmscan: do not loop on too_many_isolated for ever") -- 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