From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH] memcg: make cache index determination more robust Date: Fri, 14 Jun 2013 15:56:13 +0200 Message-ID: <20130614135613.GF10084@dhcp22.suse.cz> References: <1371069808-1172-1-git-send-email-glommer@openvz.org> <20130613163849.GL23070@dhcp22.suse.cz> <20130614112359.GC4292@localhost.localdomain> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20130614112359.GC4292@localhost.localdomain> Sender: owner-linux-mm@kvack.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Glauber Costa Cc: akpm@linux-foundation.org, linux-mm@kvack.org, cgroups@vger.kernel.org, Glauber Costa , Johannes Weiner , Kamezawa Hiroyuki On Fri 14-06-13 15:24:00, Glauber Costa wrote: > 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; > } Makes sense. You also need to test memcg == NULL, right? -- 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