From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH 1/2] gfp: add __GFP_NOACCOUNT Date: Wed, 6 May 2015 14:35:41 +0200 Message-ID: <20150506123541.GK14550@dhcp22.suse.cz> References: <20150506115941.GH14550@dhcp22.suse.cz> <20150506122431.GA29387@esperanza> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20150506122431.GA29387@esperanza> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Vladimir Davydov Cc: Andrew Morton , Johannes Weiner , Tejun Heo , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Greg Thelen , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Wed 06-05-15 15:24:31, Vladimir Davydov wrote: > On Wed, May 06, 2015 at 01:59:41PM +0200, Michal Hocko wrote: > > On Tue 05-05-15 12:45:42, Vladimir Davydov wrote: > > > Not all kmem allocations should be accounted to memcg. The following > > > patch gives an example when accounting of a certain type of allocations > > > to memcg can effectively result in a memory leak. > > > > > This patch adds the __GFP_NOACCOUNT flag which if passed to kmalloc > > > and friends will force the allocation to go through the root > > > cgroup. It will be used by the next patch. > > > > The name of the flag is way too generic. It is not clear that the > > accounting is KMEMCG related. __GFP_NO_KMEMCG sounds better? > > > > I was going to suggest doing per-cache rather than gfp flag and that > > would actually work just fine for the kmemleak as it uses its own cache > > already. But the ida_simple_get would be trickier because it doesn't use > > any special cache and more over only one user seem to have a problem so > > this doesn't sound like a good fit. > > I don't think making this flag per-cache is an option either, but for > another reason - it would not be possible to merge such a kmem cache > with caches without this flag set. As a result, total memory pressure > would increase, even for setups without kmem-active memory cgroups, > which does not sound acceptable to me. I am not sure I see the performance implications here because kmem accounted memcgs would have their copy of the cache anyway, no? Anyway, I guess it would be good to document these reasons in the changelog. > > So I do not object to opt-out for kmemcg accounting but I really think > > the name should be changed. > > I named it __GFP_NOACCOUNT to match with __GFP_NOTRACK, which is a very > specific flag too (kmemcheck), nevertheless it has a rather generic > name. __GFP_NOTRACK is a bad name IMHO as well. One has to go and check the comment to see this is kmemleak related. > Anyways, what else apart from memcg can account kmem so that we have to > mention KMEMCG in the flag name explicitly? NOACCOUNT doesn't imply kmem at all so it is not clear who is in charge of the accounting. I do not insist on __GFP_NO_KMEMCG of course but it sounds quite specific about its meaning and scope. -- Michal Hocko SUSE Labs