linux-kernel - Re: [PATCH] mm/oom_kill: revert watchdog reset in global OOM process

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Message-ID: <Z6xig5sLNpFVFU2T@tiehlicka>
Date: Wed, 12 Feb 2025 09:57:39 +0100
From: Michal Hocko <mhocko@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, yosryahmed@...gle.com,
	roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
	muchun.song@...ux.dev, davidf@...eo.com, vbabka@...e.cz,
	mkoutny@...e.com, paulmck@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	chenridong@...wei.com, wangweiyang2@...wei.com
Subject: Re: [PATCH] mm/oom_kill: revert watchdog reset in global OOM process

On Wed 12-02-25 02:57:07, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> Unlike memcg OOM, which is relatively common, global OOM events are rare
> and typically indicate that the entire system is under severe memory
> pressure. The commit ade81479c7dd ("memcg: fix soft lockup in the OOM
> process") added the touch_softlockup_watchdog in the global OOM handler to
> suppess the soft lockup issues. However, while this change can suppress
> soft lockup warnings, it does not address RCU stalls, which can still be
> detected and may cause unnecessary disturbances. Simply remove the
> modification from the global OOM handler.
> 
> Fixes: ade81479c7dd ("memcg: fix soft lockup in the OOM process")

But this is not really fixing anything, is it? While this doesn't
address a potential RCU stall it doesn't address any actual problem.
So why do we want to do this?

> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>  mm/oom_kill.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 25923cfec9c6..2d8b27604ef8 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -44,7 +44,6 @@
>  #include <linux/init.h>
>  #include <linux/mmu_notifier.h>
>  #include <linux/cred.h>
> -#include <linux/nmi.h>
>  
>  #include <asm/tlb.h>
>  #include "internal.h"
> @@ -431,15 +430,10 @@ static void dump_tasks(struct oom_control *oc)
>  		mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
>  	else {
>  		struct task_struct *p;
> -		int i = 0;
>  
>  		rcu_read_lock();
> -		for_each_process(p) {
> -			/* Avoid potential softlockup warning */
> -			if ((++i & 1023) == 0)
> -				touch_softlockup_watchdog();
> +		for_each_process(p)
>  			dump_task(p, oc);
> -		}
>  		rcu_read_unlock();
>  	}
>  }
> -- 
> 2.34.1

-- 
Michal Hocko
SUSE Labs