From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f200.google.com (mail-lj1-f200.google.com [209.85.208.200]) by kanga.kvack.org (Postfix) with ESMTP id 3E6A76B0006 for ; Wed, 1 Aug 2018 12:16:32 -0400 (EDT) Received: by mail-lj1-f200.google.com with SMTP id z24-v6so4417205lji.16 for ; Wed, 01 Aug 2018 09:16:32 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id f15-v6sor4096069ljj.73.2018.08.01.09.16.29 for (Google Transport Security); Wed, 01 Aug 2018 09:16:30 -0700 (PDT) Date: Wed, 1 Aug 2018 19:16:26 +0300 From: Vladimir Davydov Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure Message-ID: <20180801161626.j2575eru2x3lukfj@esperanza> References: <20180413113855.GI17484@dhcp22.suse.cz> <8a81c801-35c8-767d-54b0-df9f1ca0abc0@virtuozzo.com> <20180413115454.GL17484@dhcp22.suse.cz> <20180413121433.GM17484@dhcp22.suse.cz> <20180413125101.GO17484@dhcp22.suse.cz> <20180726162512.6056b5d7c1d2a5fbff6ce214@linux-foundation.org> <20180727193134.GA10996@cmpxchg.org> <20180729192621.py4znecoinw5mqcp@esperanza> <20180730153113.GB4567@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180730153113.GB4567@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Michal Hocko , Kirill Tkhai , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon, Jul 30, 2018 at 11:31:13AM -0400, Johannes Weiner wrote: > On Sun, Jul 29, 2018 at 10:26:21PM +0300, Vladimir Davydov wrote: > > On Fri, Jul 27, 2018 at 03:31:34PM -0400, Johannes Weiner wrote: > > > That said, the lifetime of the root reference on the ID is the online > > > state, we put that in css_offline. Is there a reason we need to have > > > the ID ready and the memcg in the IDR before onlining it? > > > > I fail to see any reason for this in the code. > > Me neither, thanks for double checking. > > The patch also survives stress testing cgroup creation and destruction > with the script from 73f576c04b94 ("mm: memcontrol: fix cgroup > creation failure after many small jobs"). > > > > Can we do something like this and not mess with the alloc/free > > > sequence at all? > > > > I guess so, and this definitely looks better to me. > > Cool, then I think we should merge Kirill's patch as the fix and mine > as a follow-up cleanup. > > --- > > From b4106ea1f163479da805eceada60c942bd66e524 Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Mon, 30 Jul 2018 11:03:55 -0400 > Subject: [PATCH] mm: memcontrol: simplify memcg idr allocation and error > unwinding > > The memcg ID is allocated early in the multi-step memcg creation > process, which needs 2-step ID allocation and IDR publishing, as well > as two separate IDR cleanup/unwind sites on error. > > Defer the IDR allocation until the last second during onlining to > eliminate all this complexity. There is no requirement to have the ID > and IDR entry earlier than that. And the root reference to the ID is > put in the offline path, so this matches nicely. > > Signed-off-by: Johannes Weiner Acked-by: Vladimir Davydov