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=-5.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 3057CC4320D for ; Tue, 24 Sep 2019 13:46:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EF8F32146E for ; Tue, 24 Sep 2019 13:46:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EF8F32146E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 765586B0008; Tue, 24 Sep 2019 09:46:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6EFB36B000A; Tue, 24 Sep 2019 09:46:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5DFE36B000C; Tue, 24 Sep 2019 09:46:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0067.hostedemail.com [216.40.44.67]) by kanga.kvack.org (Postfix) with ESMTP id 35C586B0008 for ; Tue, 24 Sep 2019 09:46:09 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id D2E02180AD803 for ; Tue, 24 Sep 2019 13:46:08 +0000 (UTC) X-FDA: 75969938016.06.band91_6fd3abdca8425 X-HE-Tag: band91_6fd3abdca8425 X-Filterd-Recvd-Size: 3238 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Tue, 24 Sep 2019 13:46:08 +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 C8B5BACC6; Tue, 24 Sep 2019 13:46:06 +0000 (UTC) Date: Tue, 24 Sep 2019 15:46:06 +0200 From: Michal Hocko To: Baoquan He Cc: akpm@linux-foundation.org, tj@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] memcg: Only record foreign writebacks with dirty pages when memcg is not disabled Message-ID: <20190924134606.GV23050@dhcp22.suse.cz> References: <20190923083030.6442-1-bhe@redhat.com> <20190924111138.GA31919@MiWiFi-R3L-srv> <20190924122747.GQ23050@dhcp22.suse.cz> <20190924130458.GB31919@MiWiFi-R3L-srv> <20190924131651.GR23050@dhcp22.suse.cz> <20190924134352.GC31919@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924134352.GC31919@MiWiFi-R3L-srv> 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 Tue 24-09-19 21:43:52, Baoquan He wrote: > On 09/24/19 at 03:16pm, Michal Hocko wrote: > > On Tue 24-09-19 21:04:58, Baoquan He wrote: > > > On 09/24/19 at 02:27pm, Michal Hocko wrote: > > > > On Tue 24-09-19 19:11:51, Baoquan He wrote: > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > > > index f3c15bb07cce..84e3fdb1ccb4 100644 > > > > > --- a/mm/memcontrol.c > > > > > +++ b/mm/memcontrol.c > > > > > @@ -4317,6 +4317,9 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page, > > > > > > > > > > trace_track_foreign_dirty(page, wb); > > > > > > > > > > + if (mem_cgroup_disabled()) > > > > > + return; > > > > > + > > > > > > > > This doesn't seem correct. We shouldn't even enter the slowpath with > > > > memcg disabled AFAIC. The check should be done at mem_cgroup_track_foreign_dirty > > > > level. > > > > > > You mean the way in v1 patch, right? It's also fine to me. > > > > > > I am worried about the case that memcg is enabled, the checking by > > > calling mem_cgroup_disabled() will lower efficiency. > > > > This is hidden by a static branch so I wouldn't really be worried about > > the overhead. > > > > > And it entering > > > into mem_cgroup_track_foreign_dirty_slowpath() should be a rare event. > > > > But &page->mem_cgroup->css != wb->memcg_css doesn't make any sense when > > memcg is disabled, right? > > Yeah, I think so. Make it like below? Or just put it on its own line to make the code more readable. > @@ -1261,7 +1261,8 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page, > static inline void mem_cgroup_track_foreign_dirty(struct page *page, > struct bdi_writeback *wb) > { > - if (unlikely(&page->mem_cgroup->css != wb->memcg_css)) > + if (!mem_cgroup_disabled() && > + unlikely(&page->mem_cgroup->css != wb->memcg_css)) > mem_cgroup_track_foreign_dirty_slowpath(page, wb); > } -- Michal Hocko SUSE Labs