On Tue 29-05-18 19:18:33, Michal Hocko wrote: > On Tue 29-05-18 23:33:13, Tetsuo Handa wrote: > > On 2018/05/29 17:16, Michal Hocko wrote: > > > With the full changelog. This can be either folded into the respective > > > patch or applied on top. > > > > > >>From 0bd619e7a68337c97bdaed288e813e96a14ba339 Mon Sep 17 00:00:00 2001 > > > From: Michal Hocko <mhocko@xxxxxxxx> > > > Date: Tue, 29 May 2018 10:09:33 +0200 > > > Subject: [PATCH] mm, memcg, oom: fix pre-mature allocation failures > > > > > > Tetsuo has noticed that "mm, oom: cgroup-aware OOM killer" can lead to a > > > pre-mature allocation failure if the cgroup aware oom killer is enabled > > > and select_victim_memcg doesn't pick up any memcg to kill because there > > > is a memcg already being killed. oc->chosen_memcg will become INFLIGHT_VICTIM > > > and oom_kill_memcg_victim will bail out early. oc->chosen_task will > > > stay NULL, however, and out_of_memory will therefore return false which > > > forces __alloc_pages_may_oom to not set did_some_progress and the page > > > allocator backs out and fails the allocation. > > > U > > > Fix this by checking both chosen_task and chosen_memcg in out_of_memory > > > and return false only when _both_ are NULL. > > > > I don't like this patch. It is not easy to understand and is fragile to > > future changes. Currently the only case !!oc->chosen can become false is that > > there was no eligible tasks when SysRq-f was requested or memcg OOM occurred. > > Well, the current contract is not easy unfortunatelly. We have two > different modes of operation. We are either killing whole cgroups or a > task from a cgroup. In any case, the contract says that if we have any > killable entity then at least one of chosen* is set to INFLIGHT_VICTIM. > Other than that one of them has to be !NULL or we have no eligible > killable entity. The return value reflects all these cases. Btw. if your concern is the readability then we can add a helper and decsribe all the above in the comment. -- Michal Hocko SUSE Labs
