From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26F32C3A59B for ; Mon, 2 Sep 2019 06:06:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DC2E1217D7 for ; Mon, 2 Sep 2019 06:06:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DC2E1217D7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 56D1C6B0003; Mon, 2 Sep 2019 02:06:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 51E9C6B0006; Mon, 2 Sep 2019 02:06:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 433F66B0007; Mon, 2 Sep 2019 02:06:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0109.hostedemail.com [216.40.44.109]) by kanga.kvack.org (Postfix) with ESMTP id 226F86B0003 for ; Mon, 2 Sep 2019 02:06:43 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id C083D3CEA for ; Mon, 2 Sep 2019 06:06:42 +0000 (UTC) X-FDA: 75888946644.28.pump84_3a81f2fb56a06 X-HE-Tag: pump84_3a81f2fb56a06 X-Filterd-Recvd-Size: 3389 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Mon, 2 Sep 2019 06:06:41 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id F3D79B04F; Mon, 2 Sep 2019 06:06:39 +0000 (UTC) Date: Mon, 2 Sep 2019 08:06:38 +0200 From: Michal Hocko To: Tetsuo Handa Cc: Andrew Morton , Edward Chron , Johannes Weiner , Roman Gushchin , Sergey Senozhatsky , David Rientjes , Shakeel Butt , linux-mm@kvack.org, Linus Torvalds , Petr Mladek Subject: Re: [PATCH] mm,oom: Defer dump_tasks() output. Message-ID: <20190902060638.GA14028@dhcp22.suse.cz> References: <1567159493-5232-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190830103504.GA28313@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat 31-08-19 10:03:18, Tetsuo Handa wrote: > On 2019/08/30 19:35, Michal Hocko wrote: > > On Fri 30-08-19 19:04:53, Tetsuo Handa wrote: > >> If /proc/sys/vm/oom_dump_tasks != 0, dump_header() can become very slow > >> because dump_tasks() synchronously reports all OOM victim candidates, and > >> as a result ratelimit test for dump_header() cannot work as expected. > >> > >> This patch defers dump_tasks() till oom_mutex is released. As a result of > >> this patch, the latency between out_of_memory() is called and SIGKILL is > >> sent (and the OOM reaper starts reclaiming memory) will be significantly > >> reduced. > > > > This is adding a lot of code for something that might be simply worked > > around by disabling dump_tasks. Unless there is a real world workload > > that suffers from the latency and depends on the eligible task list then > > I do not think this is mergeable. > > > > People had to use /proc/sys/vm/oom_dump_tasks == 0 (and give up obtaining some > clue) because they worried stalls caused by /proc/sys/vm/oom_dump_tasks != 0 > while they have to use /proc/sys/vm/panic_on_oom == 0 because they don't want the > down time caused by rebooting. The main qustion is whether disabling that information is actually causing any real problems. > This patch avoids stalls (and gives them some clue). > This patch also helps mitigating __ratelimit(&oom_rs) == "always true" problem. > A straightforward improvement. This is a wrong approach to mitigate that problem. Ratelimiting doesn't really work for any operation that takes a longer time. Solving that problem sounds usef in a generic way. > If there are objections we can't apply this change, reasons would be something > like "This change breaks existing userspace scripts that parse OOM messages". No, not really. There is another aspect of inclusion criterion - maintainability and code complexity. This patch doesn't help neither. -- Michal Hocko SUSE Labs