On Wed 08-05-24 20:41:35, Roman Gushchin wrote:
[...]
> @@ -1747,106 +1623,14 @@ static bool mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
>
> memcg_memory_event(memcg, MEMCG_OOM);
>
> - /*
> - * We are in the middle of the charge context here, so we
> - * don't want to block when potentially sitting on a callstack
> - * that holds all kinds of filesystem and mm locks.
> - *
> - * cgroup1 allows disabling the OOM killer and waiting for outside
> - * handling until the charge can succeed; remember the context and put
> - * the task to sleep at the end of the page fault when all locks are
> - * released.
> - *
> - * On the other hand, in-kernel OOM killer allows for an async victim
> - * memory reclaim (oom_reaper) and that means that we are not solely
> - * relying on the oom victim to make a forward progress and we can
> - * invoke the oom killer here.
> - *
> - * Please note that mem_cgroup_out_of_memory might fail to find a
> - * victim and then we have to bail out from the charge path.
> - */
> - if (READ_ONCE(memcg->oom_kill_disable)) {
> - if (current->in_user_fault) {
> - css_get(&memcg->css);
> - current->memcg_in_oom = memcg;
> - current->memcg_oom_gfp_mask = mask;
> - current->memcg_oom_order = order;
> - }
> + if (!mem_cgroup_v1_oom_prepare(memcg, mask, order, &locked))
> return false;
> - }
> -
> - mem_cgroup_mark_under_oom(memcg);
> -
> - locked = mem_cgroup_oom_trylock(memcg);
This really confused me because this looks like the oom locking is
removed for v2 but this is not the case because
mem_cgroup_v1_oom_prepare is not really v1 only code - in other words
this is not going to be just return false for CONFIG_MEMCG_V1=n.
It makes sense to move the userspace oom handling out to the v1 file. I
would keep mem_cgroup_mark_under_oom here. I am not sure about the oom
locking thing because I think we can make it v1 only. For v2 I guess we
can go without this locking as the oom path is already locked and it
implements overkilling prevention (oom_evaluate_task) as it walks all
processes in the oom hierarchy.
> -
> - if (locked)
> - mem_cgroup_oom_notify(memcg);
> -
> - mem_cgroup_unmark_under_oom(memcg);
> ret = mem_cgroup_out_of_memory(memcg, mask, order);
> -
> - if (locked)
> - mem_cgroup_oom_unlock(memcg);
> + mem_cgroup_v1_oom_finish(memcg, &locked);
>
> return ret;
> }
--
Michal Hocko
SUSE Labs
