On 18 July 2018 at 19:48, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: > On Wed, Jul 18, 2018 at 10:40 AM Bruce Merry <bmerry@xxxxxxxxx> wrote: >> > Yes, very easy to produce zombies, though I don't think kernel >> > provides any way to tell how many zombies exist on the system. >> > >> > To create a zombie, first create a memcg node, enter that memcg, >> > create a tmpfs file of few KiBs, exit the memcg and rmdir the memcg. >> > That memcg will be a zombie until you delete that tmpfs file. >> >> Thanks, that makes sense. I'll see if I can reproduce the issue. Do >> you expect the same thing to happen with normal (non-tmpfs) files that >> are sitting in the page cache, and/or dentries? >> > > Normal files and their dentries can get reclaimed while tmpfs will > stick and even if the data of tmpfs goes to swap, the kmem related to > tmpfs files will remain in memory. Sure, page cache and dentries are reclaimable given memory pressure. These machines all have more memory than they need though (64GB+) and generally don't come under any memory pressure. I'm just wondering if the behaviour we're seeing can be explained as a result of a lot of dentries sticking around (because there is no memory pressure) and in turn causing a lot of zombie cgroups to stay present until something forces reclamation of dentries. Cheers Bruce -- Bruce Merry Senior Science Processing Developer SKA South Africa
