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Date: Wed, 15 May 2024 10:45:04 +0800
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Subject: Re: [PATCH -next] memcg: don't handle event_list for v2 when
 offlining
To: Michal Hocko <mhocko@suse.com>
CC: <hannes@cmpxchg.org>, <roman.gushchin@linux.dev>,
	<shakeel.butt@linux.dev>, <muchun.song@linux.dev>,
	<akpm@linux-foundation.org>, <cgroups@vger.kernel.org>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>
References: <20240514131106.1326323-1-xiujianfeng@huawei.com>
 <ZkNwthw5vJrnQSLL@tiehlicka>
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From: xiujianfeng <xiujianfeng@huawei.com>
In-Reply-To: <ZkNwthw5vJrnQSLL@tiehlicka>
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On 2024/5/14 22:09, Michal Hocko wrote:
> On Tue 14-05-24 13:11:06, Xiu Jianfeng wrote:
>> The event_list for memcg is only valid for v1 and not used for v2,
>> so it's unnessesary to handle event_list for v2.
> 
> You are right but the code as is works just fine. The list will be
> empty. It is true that we do not need to take event_list_lock lock but
> nobody should be using this lock anyway. Also the offline callback is
> not particularly hot path. So why do we want to change the code?
> 

Actually, I don’t quite agree, but I don't insist on this patch.
Thanks for your feedback.


>>
>> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
>> ---
>>  mm/memcontrol.c | 12 +++++++-----
>>  1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index d127c9c5fabf..4254f9cd05f4 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -5881,12 +5881,14 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
>>  	 * Notify userspace about cgroup removing only after rmdir of cgroup
>>  	 * directory to avoid race between userspace and kernelspace.
>>  	 */
>> -	spin_lock_irq(&memcg->event_list_lock);
>> -	list_for_each_entry_safe(event, tmp, &memcg->event_list, list) {
>> -		list_del_init(&event->list);
>> -		schedule_work(&event->remove);
>> +	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
>> +		spin_lock_irq(&memcg->event_list_lock);
>> +		list_for_each_entry_safe(event, tmp, &memcg->event_list, list) {
>> +			list_del_init(&event->list);
>> +			schedule_work(&event->remove);
>> +		}
>> +		spin_unlock_irq(&memcg->event_list_lock);
>>  	}
>> -	spin_unlock_irq(&memcg->event_list_lock);
>>  
>>  	page_counter_set_min(&memcg->memory, 0);
>>  	page_counter_set_low(&memcg->memory, 0);
>> -- 
>> 2.34.1
>