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 -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
