From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id BC0A06B0022 for ; Tue, 20 Mar 2018 09:34:49 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id w23so890111pgv.17 for ; Tue, 20 Mar 2018 06:34:49 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 11-v6si1679175plb.658.2018.03.20.06.34.48 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 20 Mar 2018 06:34:48 -0700 (PDT) Date: Tue, 20 Mar 2018 14:34:45 +0100 From: Michal Hocko Subject: Re: [PATCH 1/2] mm,oom_reaper: Show trace of unable to reap victim thread. Message-ID: <20180320133445.GP23100@dhcp22.suse.cz> References: <1521547076-3399-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180320122818.GL23100@dhcp22.suse.cz> <201803202152.HED82804.QFOHLMVFFtOOJS@I-love.SAKURA.ne.jp> <20180320131953.GM23100@dhcp22.suse.cz> <201803202230.HDH17140.OFtMQJVLOOFHSF@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201803202230.HDH17140.OFtMQJVLOOFHSF@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: linux-mm@kvack.org, rientjes@google.com On Tue 20-03-18 22:30:16, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Tue 20-03-18 21:52:33, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > A single stack trace in the changelog would be sufficient IMHO. > > > > Appart from that. What do you expect users will do about this trace? > > > > Sure they will see a path which holds mmap_sem, we will see a bug report > > > > but we can hardly do anything about that. We simply cannot drop the lock > > > > from that path in 99% of situations. So _why_ do we want to add more > > > > information to the log? > > > > > > This case is blocked at i_mmap_lock_write(). > > > > But why does i_mmap_lock_write matter for oom_reaping. We are not > > touching hugetlb mappings. dup_mmap holds mmap_sem for write which is > > the most probable source of the backoff. > > If i_mmap_lock_write can bail out upon SIGKILL, the OOM victim will be able to > release mmap_sem held for write, which helps the OOM reaper not to back off. There are so many other blocking calls (including allocations) in dup_mmap that I do not really think i_mmap_lock_write is the biggest problem. That will be likely the case for other mmap_sem write lockers. Really I am not sure dumping more information is beneficial here. -- Michal Hocko SUSE Labs