Re: [PATCH RFC] xfs, memcg: Call xfs_fs_nr_cached_objects() only in case of global reclaim

[Kirill Tkhai]

On 15.03.2018 20:49, Michal Hocko wrote:
> On Thu 15-03-18 18:01:34, Kirill Tkhai wrote:
>> xfs_reclaim_inodes_count(XFS_M(sb)) does not care about memcg.
>> So, it's called for memcg reclaim too, e.g. this list is shrinked
>> disproportionality to another lists.
>>
>> This looks confusing, so I'm reporting about this.
>> Consider this patch as RFC.
> 
> Could you be more specific about the problem you are trying to solve?
> Because we do skip shrinkers which are not memcg aware by
> shrink_slab:
> 		/*
> 		 * If kernel memory accounting is disabled, we ignore
> 		 * SHRINKER_MEMCG_AWARE flag and call all shrinkers
> 		 * passing NULL for memcg.
> 		 */
> 		if (memcg_kmem_enabled() &&
> 		    !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
> 			continue;
> 
> Or am I missing something?

sb->s_op->nr_cached_objects is a sub-method of generic super_cache_count().
super_cache_count() is owned and only called by superblock's shrinker,
which does have SHRINKER_MEMCG_AWARE flag.

>  
>> Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
>> ---
>>  fs/xfs/xfs_super.c |    2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index 951271f57d00..124568aefa94 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -1788,6 +1788,8 @@ xfs_fs_nr_cached_objects(
>>  	struct super_block	*sb,
>>  	struct shrink_control	*sc)
>>  {
>> +	if (sc->memcg)
>> +		return 0;
>>  	return xfs_reclaim_inodes_count(XFS_M(sb));
>>  }
>>  
>