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=-11.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 7A0EEC4727D for ; Tue, 29 Sep 2020 14:29:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 19BC121531 for ; Tue, 29 Sep 2020 14:29:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="fqC5w0mG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729817AbgI2O3Y (ORCPT ); Tue, 29 Sep 2020 10:29:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:42984 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727543AbgI2O3X (ORCPT ); Tue, 29 Sep 2020 10:29:23 -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=1601389762; 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=AOGpyRKknUfTNLR63O/6b4t5RPaVPdINK6veOs+VSIU=; b=fqC5w0mGYUGWdzEzTR395xKj2x9qh6HvVHd4oGBOJ7uGMaPOeUX/r4shODLo/RhKO9zanx yZWgL9C8xkuQqNwg59h9utu8LiJ+6AoTqUVvuRE7tZPAbNjJfXLN3026zDdebCn2/OoXfi 81PaOfxjt3EM0dwPGfJp0DnqMVPPe3U= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E1C50B03D; Tue, 29 Sep 2020 14:29:21 +0000 (UTC) Date: Tue, 29 Sep 2020 16:29:20 +0200 From: Michal Hocko To: Miaohe Lin 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: <20200929142920.GD2277@dhcp22.suse.cz> References: <20200917105900.4337-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200917105900.4337-1-linmiaohe@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 */ > > Signed-off-by: Miaohe Lin > --- > mm/memcontrol.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index cd5f83de9a6f..e44f5afaf78b 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1848,10 +1848,6 @@ static void mem_cgroup_unmark_under_oom(struct mem_cgroup *memcg) > { > struct mem_cgroup *iter; > > - /* > - * When a new child is created while the hierarchy is under oom, > - * mem_cgroup_oom_lock() may not be called. Watch for underflow. > - */ > spin_lock(&memcg_oom_lock); > for_each_mem_cgroup_tree(iter, memcg) > if (iter->under_oom > 0) > -- > 2.19.1 -- Michal Hocko SUSE Labs