Re: [PATCH] memcg, oom: do not bypass oom killer for dying tasks

[Shakeel Butt <shakeel.butt@linux.dev>]

On Wed, Apr 02, 2025 at 11:27:15AM -0400, Johannes Weiner wrote:
> On Wed, Apr 02, 2025 at 11:01:17AM +0200, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > 7775face2079 ("memcg: killed threads should not invoke memcg OOM killer") has added
> > a bypass of the oom killer path for dying threads because a very
> > specific workload (described in the changelog) could hit "no killable
> > tasks" path. This itself is not fatal condition but it could be annoying
> > if this was a common case.
> > 
> > On the other hand the bypass has some issues on its own. Without
> > triggering oom killer we won't be able to trigger async oom reclaim
> > (oom_reaper) which can operate on killed tasks as well as long as they
> > still have their mm available. This could be the case during futex
> > cleanup when the memory as pointed out by Johannes in [1]. The said case
> > is still not fully understood but let's drop this bypass that was mostly
> > driven by an artificial workload and allow dying tasks to go into oom
> > path. This will make the code easier to reason about and also help
> > corner cases where oom_reaper could help to release memory.
> > 
> > [1] https://lore.kernel.org/all/20241212183012.GB1026@cmpxchg.org/T/#u
> > 
> > Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> Thanks, yeah, the investigation stalled out over the new years break
> and then... distractions.
> 
> I think we'll eventually still need the second part of [2], to force
> charge from dying OOM victims, but let's go with this for now.

Agreed.

> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> 
> [2] https://lore.kernel.org/all/20241212183012.GB1026@cmpxchg.org/
> 

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>