On Fri 02-11-18 16:22:41, Roman Gushchin wrote: > On Fri, Nov 02, 2018 at 05:13:14PM +0100, Michal Hocko wrote: > > On Fri 02-11-18 15:48:57, Roman Gushchin wrote: > > > On Fri, Nov 02, 2018 at 09:03:55AM +0100, Michal Hocko wrote: > > > > On Fri 02-11-18 02:45:42, Dexuan Cui wrote: > > > > [...] > > > > > I totally agree. I'm now just wondering if there is any temporary workaround, > > > > > even if that means we have to run the kernel with some features disabled or > > > > > with a suboptimal performance? > > > > > > > > One way would be to disable kmem accounting (cgroup.memory=nokmem kernel > > > > option). That would reduce the memory isolation because quite a lot of > > > > memory will not be accounted for but the primary source of in-flight and > > > > hard to reclaim memory will be gone. > > > > > > In my experience disabling the kmem accounting doesn't really solve the issue > > > (without patches), but can lower the rate of the leak. > > > > This is unexpected. 90cbc2508827e was introduced to address offline > > memcgs to be reclaim even when they are small. But maybe you mean that > > we still leak in an absence of the memory pressure. Or what does prevent > > memcg from going down? > > There are 3 independent issues which are contributing to this leak: > 1) Kernel stack accounting weirdness: processes can reuse stack accounted to > different cgroups. So basically any running process can take a reference to any > cgroup. yes, but kmem accounting should rule that out, right? If not then this is a clear bug and easy to backport because that would mean to add a missing memcg_kmem_enabled check. > 2) We do forget to scan the last page in the LRU list. So if we ended up with > 1-page long LRU, it can stay there basically forever. Why /* * If the cgroup's already been deleted, make sure to * scrape out the remaining cache. */ if (!scan && !mem_cgroup_online(memcg)) scan = min(size, SWAP_CLUSTER_MAX); in get_scan_count doesn't work for that case? > 3) We don't apply enough pressure on slab objects. again kmem accounting disabled should make this moot > Because one reference is enough to keep the entire memcg structure in place, > we really have to close all three to eliminate the leak. Disabling kmem > accounting mitigates only the last one. -- Michal Hocko SUSE Labs
