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

Chen Ridong
2025-02-12T09:19:31Z

On 2025/2/12 16:57, Michal Hocko wrote:
> On Wed 12-02-25 02:57:07, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@huawei.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@huawei.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
>