From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) by kanga.kvack.org (Postfix) with ESMTP id 4BDBB6B0005 for ; Tue, 31 Jul 2018 19:39:12 -0400 (EDT) Received: by mail-pg1-f200.google.com with SMTP id a26-v6so9984430pgw.7 for ; Tue, 31 Jul 2018 16:39:12 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id f8-v6si14328601plb.381.2018.07.31.16.39.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 31 Jul 2018 16:39:11 -0700 (PDT) Date: Tue, 31 Jul 2018 16:39:08 -0700 From: Andrew Morton Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure Message-Id: <20180731163908.603d7a27c6534341e1afa724@linux-foundation.org> In-Reply-To: <20180730153113.GB4567@cmpxchg.org> References: <6dbc33bb-f3d5-1a46-b454-13c6f5865fcd@virtuozzo.com> <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-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Vladimir Davydov , Michal Hocko , Kirill Tkhai , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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);