Re: [PATCH] mm/vmscan: add pgstall to memcg

[Chuyi Zhou <zhouchuyi@bytedance.com>]

在 2022/6/25 上午4:42, Andrew Morton 写道:
> (cc memcg developers)
> On Thu, 23 Jun 2022 16:01:03 +0800 zhouchuyi <zhouchuyi@bytedance.com> wrote:
> 
>> Add pgstall to indicate the times of entering direct reclaim of memcg, use
>> the item of ALLOCSTALL_NORMAL in vmevents to save the data.
>>
>> Signed-off-by: zhouchuyi <zhouchuyi@bytedance.com>
>> ---
>>
>>
>> Hi，
>>
>> I notice memcg uses some items to indicate the situation of direct reclaim in memory.stat，such as pgsteal and pgscan.
>> I think there is no harm in adding another item to show the times of entering direct reclaim.
>>
> 
> Why do you consider this useful?  Do you have a use case?  If so,
> please describe it in detail.
> 
Since there are allocstall in proc/vmstat which indicate the number of 
entering direct reclaim of !cgroup_reclaim, So I think it maybe useful. 
For example, users could adjust memory.max to prevent entering direct 
reclaim through this item.So what do you think about it ?
>>
>> ...
>>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index 176298f2f..44c5b15bd 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -1447,8 +1447,11 @@ PAGE_SIZE multiple when read back.
>>   
>>   	  pgsteal (npn)
>>   		Amount of reclaimed pages
>> -
>> -	  pgactivate (npn)
>> +
>> +          pgstall (npn)
>> +	  	Number of entering direct reclaim
>> +	
>> +          pgactivate (npn)
>>   		Amount of pages moved to the active LRU list
>>   
>>   	  pgdeactivate (npn)
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index abec50f31..f407084b2 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1505,6 +1505,8 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
>>   	seq_buf_printf(&s, "pgscan %lu\n",
>>   		       memcg_events(memcg, PGSCAN_KSWAPD) +
>>   		       memcg_events(memcg, PGSCAN_DIRECT));
>> +	seq_buf_printf(&s, "pgstall %lu\n",
>> +			   memcg_events(memcg, ALLOCSTALL_NORMAL));
>>   	seq_buf_printf(&s, "pgsteal %lu\n",
>>   		       memcg_events(memcg, PGSTEAL_KSWAPD) +
>>   		       memcg_events(memcg, PGSTEAL_DIRECT));
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index f7d9a683e..107cec59a 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -3532,7 +3532,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>>   
>>   	if (!cgroup_reclaim(sc))
>>   		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
>> -
>> +	else {
>> +		count_memcg_events(sc->target_mem_cgroup,
>> +					ALLOCSTALL_NORMAL, 1);
>> +	}
>>   	do {
>>   		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
>>   				sc->priority);
>> -- 
>> 2.20.1