Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753308AbcCLEIM (ORCPT ); Fri, 11 Mar 2016 23:08:12 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:38706 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751917AbcCLEIJ (ORCPT ); Fri, 11 Mar 2016 23:08:09 -0500 To: mhocko@kernel.org Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org, hannes@cmpxchg.org, mgorman@suse.de, rientjes@google.com, hillf.zj@alibaba-inc.com, kamezawa.hiroyu@jp.fujitsu.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/3] OOM detection rework v4 From: Tetsuo Handa References: <201603112232.AEJ78150.LOHQJtMFSVOFOF@I-love.SAKURA.ne.jp> <20160311152851.GU27701@dhcp22.suse.cz> <201603120149.JEI86913.JVtSOOFHMFFQOL@I-love.SAKURA.ne.jp> <20160311170022.GX27701@dhcp22.suse.cz> <201603120220.GFJ00000.QOLVOtJOMFFSHF@I-love.SAKURA.ne.jp> In-Reply-To: <201603120220.GFJ00000.QOLVOtJOMFFSHF@I-love.SAKURA.ne.jp> Message-Id: <201603121308.FEH04174.OFHLOFMSJOtQVF@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Sat, 12 Mar 2016 13:08:04 +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 Content-Length: 1975 Lines: 34 Michal Hocko wrote: > OK, that would suggest that the oom rework patches are not really > related. They just moved from the livelock to a sleep which is good in > general IMHO. We even know that it is most probably the IO that is the > problem because we know that more than half of the reclaimable memory is > either dirty or under writeback. That is where you should be looking. > Why the IO is not making progress or such a slow progress. > A footnote. Regarding this reproducer, the problem was "anybody can declare OOM and call out_of_memory(). But out_of_memory() does nothing because there is a thread which has TIF_MEMDIE." before the OOM detection rework patches, and the problem is "nobody can declare OOM and call out_of_memory(). Although out_of_memory() will do nothing because there is a thread which has TIF_MEMDIE." after the OOM detection rework patches. Dave Chinner wrote at http://lkml.kernel.org/r/20160211225929.GU14668@dastard : > > Although there are memory allocating tasks passing gfp flags with > > __GFP_KSWAPD_RECLAIM, kswapd is unable to make forward progress because > > it is blocked at down() called from memory reclaim path. And since it is > > legal to block kswapd from memory reclaim path (am I correct?), I think > > we must not assume that current_is_kswapd() check will break the infinite > > loop condition. > > Right, the threads that are blocked in writeback waiting on memory > reclaim will be using GFP_NOFS to prevent recursion deadlocks, but > that does not avoid the problem that kswapd can then get stuck > on those locks, too. Hence there is no guarantee that kswapd can > make reclaim progress if it does dirty page writeback... Unless we address the issue Dave commented, the OOM detection rework patches add a new location of livelock (which is demonstrated by this reproducer) in the memory allocator. It is an unfortunate change that we add a new location of livelock when we are trying to solve thrashing problem.