From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx204.postini.com [74.125.245.204]) by kanga.kvack.org (Postfix) with SMTP id E28B46B003A for ; Fri, 14 Jun 2013 07:24:05 -0400 (EDT) Received: by mail-la0-f47.google.com with SMTP id fe20so417946lab.20 for ; Fri, 14 Jun 2013 04:24:04 -0700 (PDT) Date: Fri, 14 Jun 2013 15:24:00 +0400 From: Glauber Costa Subject: Re: [PATCH] memcg: make cache index determination more robust Message-ID: <20130614112359.GC4292@localhost.localdomain> References: <1371069808-1172-1-git-send-email-glommer@openvz.org> <20130613163849.GL23070@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130613163849.GL23070@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, cgroups@vger.kernel.org, Glauber Costa , Johannes Weiner , Kamezawa Hiroyuki On Thu, Jun 13, 2013 at 06:38:49PM +0200, Michal Hocko wrote: > On Wed 12-06-13 16:43:28, Glauber Costa wrote: > > I caught myself doing something like the following outside memcg core: > > > > memcg_id = -1; > > if (memcg && memcg_kmem_is_active(memcg)) > > memcg_id = memcg_cache_id(memcg); > > > > to be able to handle all possible memcgs in a sane manner. In particular, the > > root cache will have kmemcg_id = -1 (just because we don't call memcg_kmem_init > > to the root cache since it is not limitable). We have always coped with that by > > making sure we sanitize which cache is passed to memcg_cache_id. Although this > > example is given for root, what we really need to know is whether or not a > > cache is kmem active. > > > > But outside the memcg core testing for root, for instance, is not trivial since > > we don't export mem_cgroup_is_root. I ended up realizing that this tests really > > belong inside memcg_cache_id. This patch moves the tests inside memcg_cache_id > > and make sure it always return a meaningful value. > > This is quite a mess, to be honest. Some callers test/require > memcg_can_account_kmem others !p->is_root_cache. Can we have that > unified, please? > > Also the return value of this function is used mostly as an index to > memcg_params->memcg_caches array so returning -1 sounds like a bad idea. > Few other cases use it as a real id. Maybe we need to split this up. > > Pulling the check inside the function is OK but can we settle with a > common pattern here, pretty please? > BTW: Since the test for memcg_can_account_kmem is a bit stronger than memcg_kmem_is_active (the difference is that it tests the extra bit that we need to coordinate the static branches), I will test for that, instead. Like this: int memcg_cache_id(struct mem_cgroup *memcg) { if (!memcg_can_account_kmem(memcg)) return -1; return memcg->kmemcg_id; } This will allow us to consolidate the tests around it a bit in my follow up patch. > > Signed-off-by: Glauber Costa > > Cc: Johannes Weiner > > Cc: Michal Hocko > > Cc: Kamezawa Hiroyuki > > --- > > mm/memcontrol.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 2e851f4..749f7a4 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -3081,7 +3081,9 @@ void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep) > > */ > > int memcg_cache_id(struct mem_cgroup *memcg) > > { > > - return memcg ? memcg->kmemcg_id : -1; > > + if (!memcg || !memcg_kmem_is_active(memcg)) > > + return -1; > > + return memcg->kmemcg_id; > > } > > > > /* > > -- > > 1.8.1.4 > > > > -- > Michal Hocko > SUSE Labs -- 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