From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754617AbcFPUGV (ORCPT ); Thu, 16 Jun 2016 16:06:21 -0400 Received: from mail-yw0-f194.google.com ([209.85.161.194]:36248 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753992AbcFPUGT (ORCPT ); Thu, 16 Jun 2016 16:06:19 -0400 Date: Thu, 16 Jun 2016 16:06:17 -0400 From: Tejun Heo To: Johannes Weiner Cc: Andrew Morton , Vladimir Davydov , Michal Hocko , Li Zefan , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm: memcontrol: fix cgroup creation failure after many small jobs Message-ID: <20160616200617.GD3262@mtj.duckdns.org> References: <20160616034244.14839-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160616034244.14839-1-hannes@cmpxchg.org> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Looks generally good to me. Some comments below. On Wed, Jun 15, 2016 at 11:42:44PM -0400, Johannes Weiner wrote: > @@ -6205,6 +6205,24 @@ struct cgroup *cgroup_get_from_path(const char *path) > } > EXPORT_SYMBOL_GPL(cgroup_get_from_path); > > +/** > + * css_id_free - relinquish an existing CSS's ID > + * @css: the CSS > + * > + * This releases the @css's ID and allows it to be recycled while the > + * CSS continues to exist. This is useful for controllers with state > + * that extends past a cgroup's lifetime but doesn't need precious ID > + * address space. > + * > + * This invalidates @css->id, and css_from_id() might return NULL or a > + * new css if the ID has been recycled in the meantime. > + */ > +void css_id_free(struct cgroup_subsys_state *css) > +{ > + cgroup_idr_remove(&css->ss->css_idr, css->id); > + css->id = 0; > +} I don't quite get why we're trying to free css->id earlier when memcg is gonna be using its private id anyway. From cgroup core side, the id space isn't restricted. > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 75e74408cc8f..1d8a6dffdc25 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c ... > +static void mem_cgroup_id_put(struct mem_cgroup *memcg) > +{ > + if (atomic_dec_and_test(&memcg->id.ref)) { > + idr_remove(&mem_cgroup_idr, memcg->id.id); Maybe this should do "memcg->id.id = 0"? > + css_id_free(&memcg->css); > + css_put(&memcg->css); > + } > +} > + > +/** > + * mem_cgroup_from_id - look up a memcg from a memcg id > + * @id: the memcg id to look up > + * > + * Caller must hold rcu_read_lock(). > + */ > +struct mem_cgroup *mem_cgroup_from_id(unsigned short id) > +{ > + WARN_ON_ONCE(!rcu_read_lock_held()); > + return id > 0 ? idr_find(&mem_cgroup_idr, id) : NULL; > +} css_from_id() has it too but I don't think id > 0 test is necessary. We prolly should take it out of css_from_id() too. It might be useful to add comment explaining why memcg needs private ids. Thanks. -- tejun