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

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Message-ID: <bccc9e06-af8b-4a55-a69c-98596f1c1385@suse.cz>
Date: Wed, 12 Feb 2025 10:34:06 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Chen Ridong <chenridong@...weicloud.com>, 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, 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 2/12/25 10:19, Chen Ridong wrote:
> 
> 
> 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?

I suggested that part doesn't need to be in the patch, but if it was merged
with it, we can just leave it there. Thanks.