linux-kernel - Re: [PATCH] mm: Mark the OOM reaper thread as freezable

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Date:   Mon, 20 Sep 2021 14:40:37 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Sultan Alsawaf <sultan@...neltoast.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Mark the OOM reaper thread as freezable

On Sat 18-09-21 16:39:20, Sultan Alsawaf wrote:
> From: Sultan Alsawaf <sultan@...neltoast.com>
> 
> The OOM reaper thread uses wait_event_freezable() without actually being
> marked as freezable. Fix it by adding a set_freezable() call.

What is the actual problem you are trying to solve here. Freezer details
are hairy and I have to re-learn them each time again and again but from
what I remember wait_event_freezable doesn't really depend on tyask
being freezable. It tells the freezer that the task is OK to exclude
while it is sleeping and that should be just the case for the oom
reaper. Or am I missing something?
 
> Fixes: aac453635549 ("mm, oom: introduce oom reaper")
> Signed-off-by: Sultan Alsawaf <sultan@...neltoast.com>
> ---
>  mm/oom_kill.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 831340e7ad8b..46a742b57735 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -641,6 +641,8 @@ static void oom_reap_task(struct task_struct *tsk)
>  
>  static int oom_reaper(void *unused)
>  {
> +	set_freezable();
> +
>  	while (true) {
>  		struct task_struct *tsk = NULL;
>  
> -- 
> 2.33.0

-- 
Michal Hocko
SUSE Labs