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

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Message-ID: <d264a73e-966f-4890-9e23-88d476f0fc81@huaweicloud.com>
Date: Wed, 12 Feb 2025 17:19:16 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Michal Hocko <mhocko@...e.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 2025/2/12 16:57, Michal Hocko wrote:
> 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?
> 


[1]
https://lore.kernel.org/cgroups/0d9ea655-5c1a-4ba9-9eeb-b45d74cc68d0@huaweicloud.com/

As previously discussed, the work I have done on the global OOM is 'half
of the job'. Based on our discussions, I thought that it would be best
to abandon this approach for global OOM. Therefore, I am sending this
patch to revert the changes.

Or just leave it?

Best regards,
Ridong

>> 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
>