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=-5.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 E8BA0C47420 for ; Wed, 30 Sep 2020 08:43:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 950F22075F for ; Wed, 30 Sep 2020 08:43:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="VfV4dAj7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728618AbgI3Inq (ORCPT ); Wed, 30 Sep 2020 04:43:46 -0400 Received: from mx2.suse.de ([195.135.220.15]:43014 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725836AbgI3Inq (ORCPT ); Wed, 30 Sep 2020 04:43:46 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1601455424; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QhiptoBURkg4uq4dMDHGe+8biN2SOcQktd4lq8iMzC4=; b=VfV4dAj7zRnkAOtH9oe2lFoD+GI1LiJPXeQl9iW87xGUeS7/HL4Tf4zh4DG4lZqyanotic qxviOA9fNLmmfV8/5czDMQKDRRwCGC00zf4qsG5MwCLidLYExCBcKV5pKVfCRjRESXR7iK CkDeAVlzxX3OD7eMMZSQ3noEWtrfLEE= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0DEE1AB0E; Wed, 30 Sep 2020 08:43:44 +0000 (UTC) Date: Wed, 30 Sep 2020 10:43:43 +0200 From: Michal Hocko To: linmiaohe Cc: "hannes@cmpxchg.org" , "vdavydov.dev@gmail.com" , "akpm@linux-foundation.org" , "cgroups@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] mm: memcontrol: remove obsolete comment of mem_cgroup_unmark_under_oom() Message-ID: <20200930084343.GO2277@dhcp22.suse.cz> References: <7d1ea112d8a740cab555eaf7be530286@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7d1ea112d8a740cab555eaf7be530286@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 30-09-20 01:34:25, linmiaohe wrote: > Michal Hocko wrote: > > On Thu 17-09-20 06:59:00, Miaohe Lin wrote: > >> Since commit 79dfdaccd1d5 ("memcg: make oom_lock 0 and 1 based rather > >> than counter"), the mem_cgroup_unmark_under_oom() is added and the > >> comment of the mem_cgroup_oom_unlock() is moved here. But this comment > >> make no sense here because mem_cgroup_oom_lock() does not operate on under_oom field. > > > >OK, so I've looked into this more deeply and I finally remember why we have this comment here. The point is that under_oom shouldn't underflow and that we have to explicitly check for > 0 because a new child memcg could have been added between mem_cgroup_mark_under_oom and mem_cgroup_unmark_under_oom. > > > >So the comment makes sense although it is not as helpful as it could be. > >I think that changing it to the following will be more usefule > > > > /* > > * Be careful about under_oom underflows becase a child memcg > > * could have neem added after mem_cgroup_mark_under_oom > > Should it be s/neem/been/ ? yep, fat fingers... > > > */ > > Many thanks for detailed explanation. Will fix it in v2. Thanks again. -- Michal Hocko SUSE Labs