From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 77BF26B0008 for ; Thu, 2 Aug 2018 04:03:10 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id y8-v6so500157edr.12 for ; Thu, 02 Aug 2018 01:03:10 -0700 (PDT) Received: from EUR01-HE1-obe.outbound.protection.outlook.com (mail-he1eur01on0112.outbound.protection.outlook.com. [104.47.0.112]) by mx.google.com with ESMTPS id a16-v6si1711776edc.228.2018.08.02.01.03.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 02 Aug 2018 01:03:08 -0700 (PDT) Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure References: <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> <20180731163908.603d7a27c6534341e1afa724@linux-foundation.org> <20180801155552.GA8600@cmpxchg.org> <20180801162235.j3v7xipyw5afnj4x@esperanza> From: Kirill Tkhai Message-ID: <7a836e47-f0a4-6802-9b90-cc473e5ab90b@virtuozzo.com> Date: Thu, 2 Aug 2018 11:03:02 +0300 MIME-Version: 1.0 In-Reply-To: <20180801162235.j3v7xipyw5afnj4x@esperanza> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov , Johannes Weiner Cc: Andrew Morton , Michal Hocko , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 01.08.2018 19:22, Vladimir Davydov wrote: > On Wed, Aug 01, 2018 at 11:55:52AM -0400, Johannes Weiner wrote: >> On Tue, Jul 31, 2018 at 04:39:08PM -0700, Andrew Morton wrote: >>> On Mon, 30 Jul 2018 11:31:13 -0400 Johannes Weiner wrote: >>> >>>> 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. >>> >>> This patch isn't aware of Kirill's later "mm, memcg: assign memcg-aware >>> shrinkers bitmap to memcg", which altered mem_cgroup_css_online(): >>> >>> @@ -4356,6 +4470,11 @@ static int mem_cgroup_css_online(struct >>> { >>> struct mem_cgroup *memcg = mem_cgroup_from_css(css); >>> >>> + if (memcg_alloc_shrinker_maps(memcg)) { >>> + mem_cgroup_id_remove(memcg); >>> + return -ENOMEM; >>> + } >>> + >>> /* Online state pins memcg ID, memcg ID pins CSS */ >>> atomic_set(&memcg->id.ref, 1); >>> css_get(css); >>> >> >> Hm, that looks out of place too. The bitmaps are allocated for the >> entire lifetime of the css, not just while it's online. >> >> Any objections to the following fixup to that patch? > > That would be incorrect. Memory cgroups that haven't been put online > are invisible to for_each_mem_cgroup(), which is used for expanding > shrinker maps of all cgroups - see memcg_expand_shrinker_maps(). So if > memcg_expand_shrinker_maps() is called between css_alloc and css_online, > it will miss this cgroup and its shrinker_map won't be reallocated to > fit the new id. Allocating the shrinker map in css_online guarantees > that it won't happen. Yes, doubtless. >Looks like this code lacks a comment... Ok.