linux-kernel - Re: [PATCH 1/3] mm/memcg: Fix min/low usage in propagate_protected

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Date:   Mon, 3 Dec 2018 22:49:18 +0800
From:   Xunlei Pang <xlpang@...ux.alibaba.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] mm/memcg: Fix min/low usage in
 propagate_protected_usage()

On 2018/12/3 下午7:54, Michal Hocko wrote:
> On Mon 03-12-18 16:01:17, Xunlei Pang wrote:
>> When usage exceeds min, min usage should be min other than 0.
>> Apply the same for low.
> 
> Why? What is the actual problem.

children_min_usage tracks the total children usages under min,
it's natural that min should be added into children_min_usage
when above min, I can't image why 0 is added, is there special
history I missed?

See mem_cgroup_protected(), when usage exceeds min, emin is
calculated as "parent_emin*min/children_min_usage".

> 
>> Signed-off-by: Xunlei Pang <xlpang@...ux.alibaba.com>
>> ---
>>  mm/page_counter.c | 12 ++----------
>>  1 file changed, 2 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/page_counter.c b/mm/page_counter.c
>> index de31470655f6..75d53f15f040 100644
>> --- a/mm/page_counter.c
>> +++ b/mm/page_counter.c
>> @@ -23,11 +23,7 @@ static void propagate_protected_usage(struct page_counter *c,
>>  		return;
>>  
>>  	if (c->min || atomic_long_read(&c->min_usage)) {
>> -		if (usage <= c->min)
>> -			protected = usage;
>> -		else
>> -			protected = 0;
>> -
>> +		protected = min(usage, c->min);
>>  		old_protected = atomic_long_xchg(&c->min_usage, protected);
>>  		delta = protected - old_protected;
>>  		if (delta)
>> @@ -35,11 +31,7 @@ static void propagate_protected_usage(struct page_counter *c,
>>  	}
>>  
>>  	if (c->low || atomic_long_read(&c->low_usage)) {
>> -		if (usage <= c->low)
>> -			protected = usage;
>> -		else
>> -			protected = 0;
>> -
>> +		protected = min(usage, c->low);
>>  		old_protected = atomic_long_xchg(&c->low_usage, protected);
>>  		delta = protected - old_protected;
>>  		if (delta)
>> -- 
>> 2.13.5 (Apple Git-94)
>>
>