Re: [PATCH V8 1/2] mm: memcg softlimit reclaim rework

[Rik van Riel <riel@redhat.com>]

On 08/03/2012 11:22 AM, Michal Hocko wrote:
> On Thu 02-08-12 14:24:18, Ying Han wrote:
> [...]
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 3e0d0cd..88487b3 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1866,7 +1866,22 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
>>   	do {
>>   		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
>>
>> -		shrink_lruvec(lruvec, sc);
>> +		/*
>> +		 * Reclaim from mem_cgroup if any of these conditions are met:
>> +		 * - this is a targetted reclaim ( not global reclaim)
>> +		 * - reclaim priority is less than DEF_PRIORITY
>> +		 * - mem_cgroup or its ancestor ( not including root cgroup)
>> +		 * exceeds its soft limit
>> +		 *
>> +		 * Note: The priority check is a balance of how hard to
>> +		 * preserve the pages under softlimit. If the memcgs of the
>> +		 * zone having trouble to reclaim pages above their softlimit,
>> +		 * we have to reclaim under softlimit instead of burning more
>> +		 * cpu cycles.
>> +		 */
>> +		if (!global_reclaim(sc) || sc->priority<  DEF_PRIORITY ||
>> +				mem_cgroup_over_soft_limit(memcg))
>> +			shrink_lruvec(lruvec, sc);
>>
>>   		/*
>>   		 * Limit reclaim has historically picked one memcg and
>
> I am thinking that we could add a constant for the priority
> limit. Something like
> #define MEMCG_LOW_SOFTLIMIT_PRIORITY	DEF_PRIORITY
>
> Although it doesn't seem necessary at the moment, because there is just
> one location where it matters but it could help in the future.
> What do you think?

I am working on changing the code to find the "highest priority"
LRU and reclaim from that list first.  That will obviate the need
for such a change. However, the other cleanups and simplifications
made by Ying's patch are good to have...

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