Re: [PATCH] mm: delay oom_reaper only for the process using robust-futex

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

Hi Zhongjinji,

On Thu, Jul 31, 2025 at 06:29:04PM +0800, zhongjinji@honor.com wrote:
> From: zhongjinji <zhongjinji@honor.com>
> 
> After the patch here:
> https://lore.kernel.org/all/20220414144042.677008-1-npache@redhat.com/T/#u
> was merged, the oom_reaper almost stops working.

Can you expand on this? How exactly it stopped working? Is this due to
oom-killed processes are exiting in timely fashion or are you seeing the
system remains in memory pressure state longer?

> 
> But I noticed that many processes do not use robust-futex, so they don’t
> access user-space memory during do_exit and don’t run into the problem
> mentioned in that patch.
> 
> So, this change delays the oom_reaper only when the process uses
> robust-futex, letting the oom_reaper work properly in more cases.

The direction seems reasonable.

>  
> +static inline bool exit_may_access_user(struct task_struct *task)
> +{
> +	return task->robust_list || task->compat_robust_list;

Here I am not sure. This robust_list seems like a per-task list and we
are making a process level decision based on a given task's usage of
robust list. Can we have a scenario where some tasks/threads of a
process does not have robust list and others have? If yes this can cause
similar similar which the original patch tried to solve, right?