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Subject: Re: [PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API
To:     Michal Hocko <mhocko@kernel.org>
Cc:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <1581398649-125989-1-git-send-email-yang.shi@linux.alibaba.com>
 <1581398649-125989-2-git-send-email-yang.shi@linux.alibaba.com>
 <20200212082346.GB11353@dhcp22.suse.cz>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <94323469-c9d5-33ab-318b-2677dd966a92@linux.alibaba.com>
Date:   Wed, 12 Feb 2020 19:18:59 -0800
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On 2/12/20 12:23 AM, Michal Hocko wrote:
> On Tue 11-02-20 13:24:09, Yang Shi wrote:
>> Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
>> open coding.
> Yes, the direct use outside of memcontrol.c should be really an
> exception. The only other similar case is cgwb_bdi_init and there is no
> easy way to replace - except for adding a helper which is not worth it.

Yes, it seems so. cgwb_bdi_init just deferences root_mem_cgroup to 
access its css. It is the only user outside memcontrol.c, so I agree a 
helper for it might be overkilling. Once we have more users, it should 
be considered.

>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks.

>
> Thanks!
>
>> ---
>>   mm/vmpressure.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
>> index 0590f00..d69019f 100644
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -280,7 +280,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>>   		enum vmpressure_levels level;
>>   
>>   		/* For now, no users for root-level efficiency */
>> -		if (!memcg || memcg == root_mem_cgroup)
>> +		if (!memcg || mem_cgroup_is_root(memcg))
>>   			return;
>>   
>>   		spin_lock(&vmpr->sr_lock);
>> -- 
>> 1.8.3.1
>>