From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f69.google.com (mail-lf0-f69.google.com [209.85.215.69]) by kanga.kvack.org (Postfix) with ESMTP id AB0D16B0005 for ; Fri, 17 Jun 2016 12:25:44 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id l184so1795358lfl.3 for ; Fri, 17 Jun 2016 09:25:44 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id p4si534679wjz.184.2016.06.17.09.25.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Jun 2016 09:25:43 -0700 (PDT) Date: Fri, 17 Jun 2016 12:23:10 -0400 From: Johannes Weiner Subject: Re: [PATCH] mm: memcontrol: fix cgroup creation failure after many small jobs Message-ID: <20160617162310.GA19084@cmpxchg.org> References: <20160616034244.14839-1-hannes@cmpxchg.org> <20160616200617.GD3262@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160616200617.GD3262@mtj.duckdns.org> Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo 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 On Thu, Jun 16, 2016 at 04:06:17PM -0400, Tejun Heo wrote: > 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. For some reason I was thinking of CSS ID being restricted as well, but of course the only restriction is what's enforced in memcg onlining. I deleted it. > > 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"? Added. > > + 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. Yeah, idr_find() just returns NULL for index 0 - no warning. I removed it from my patch and added a patch to remove it in css_from_id(). > It might be useful to add comment explaining why memcg needs private > ids. Good point. I put an intro comment above the mem_cgroup_idr definition that explains why we need a private space. Thanks -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org