Re: [PATCH v2 1/3] mm: Fix dropped memcg from mem cgroup soft limit tree

[Tim Chen]

On 2/18/21 11:13 AM, Michal Hocko wrote:

> 
> Fixes: 4e41695356fb ("memory controller: soft limit reclaim on contention")
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> 
> Thanks!
>> ---
>>  mm/memcontrol.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index ed5cc78a8dbf..a51bf90732cb 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -3505,8 +3505,12 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>>  			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
>>  			break;
>>  	} while (!nr_reclaimed);
>> -	if (next_mz)
>> +	if (next_mz) {
>> +		spin_lock_irq(&mctz->lock);
>> +		__mem_cgroup_insert_exceeded(next_mz, mctz, excess);
>> +		spin_unlock_irq(&mctz->lock);
>>  		css_put(&next_mz->memcg->css);
>> +	}
>>  	return nr_reclaimed;
>>  }
>>  
>> -- 
>> 2.20.1
> 

Mel,

Reviewing this patch a bit more, I realize that there is a chance that the removed
next_mz could be inserted back to the tree from a memcg_check_events
that happen in between.  So we need to make sure that the next_mz
is indeed off the tree and update the excess value before adding it
back.  Update the patch to the patch below.

Thanks.

Tim
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