On 08.08.2018 15:36, Tetsuo Handa wrote: > On 2018/08/08 20:51, Kirill Tkhai wrote: >> @@ -192,7 +193,6 @@ static int prealloc_memcg_shrinker(struct shrinker >> *shrinker) >> int id, ret = -ENOMEM; >> >> down_write(&shrinker_rwsem); >> - /* This may call shrinker, so it must use down_read_trylock() */ >> id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL); >> if (id < 0) >> goto unlock; > > I don't know why perf reports down_read_trylock(&shrinker_rwsem).
This happens in the case of many cgroups and mounts on node. This is often happen on the big machines with containers. > But above code is already bad. GFP_KERNEL allocation involves shrinkers and > the OOM killer would be invoked because shrinkers are defunctional due to > this down_write(&shrinker_rwsem). Please avoid blocking memory allocation > with shrinker_rwsem held. There was non-blocking allocation in first versions of the patchset, but it's gone away in the process of the review (CC Vladimir). There are still pages lists shrinkers in case of shrink_slab() is not available, while additional locks makes the code more difficult and not worth this difficulties. Kirill
