Re: [PATCH] mm thp: shrink deferred split THPs harder

[Michal Hocko]

On Wed 02-10-19 07:56:50, Yang Shi wrote:
> The deferred split THPs may get accumulated with some workloads, they
> would get shrunk when memory pressure is hit.  Now we use DEFAULT_SEEKS
> to determine how many objects would get scanned then split if possible,
> but actually they are not like other system cache objects, i.e. inode
> cache which would incur extra I/O if over reclaimed, the unmapped pages
> will not be accessed anymore, so we could shrink them more aggressively.
> 
> We could shrink THPs more pro-actively even though memory pressure is not
> hit, however, IMHO waiting for memory pressure is still a good
> compromise and trade-off.  And, we do have simpler ways to shrink these
> objects harder until we have to take other means do pro-actively drain.
> 
> Change shrinker->seeks to 0 to shrink deferred split THPs harder.

Do you have any numbers on the effect of this patch.

Btw. the whole thing is getting more and more complex and I still
believe the approach is just wrong. We are tunning for something that
doesn't really belong to the memory reclaim in the first place IMHO.
 
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
>  mm/huge_memory.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 3b78910..1d6b1f1 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2955,7 +2955,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>  static struct shrinker deferred_split_shrinker = {
>  	.count_objects = deferred_split_count,
>  	.scan_objects = deferred_split_scan,
> -	.seeks = DEFAULT_SEEKS,
> +	.seeks = 0,
>  	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
>  		 SHRINKER_NONSLAB,
>  };
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs