Re: [PATCH] mm: slowly shrink slabs with a relatively small number of objects

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

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On Fri, 2018-08-31 at 13:34 -0700, Roman Gushchin wrote:

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index fa2c150ab7b9..c910cf6bf606 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -476,6 +476,10 @@ static unsigned long do_shrink_slab(struct
> shrink_control *shrinkctl,
>  	delta = freeable >> priority;
>  	delta *= 4;
>  	do_div(delta, shrinker->seeks);
> +
> +	if (delta == 0 && freeable > 0)
> +		delta = min(freeable, batch_size);
> +
>  	total_scan += delta;
>  	if (total_scan < 0) {
>  		pr_err("shrink_slab: %pF negative objects to delete
> nr=%ld\n",

I agree that we need to shrink slabs with fewer than
4096 objects, but do we want to put more pressure on
a slab the moment it drops below 4096 than we applied
when it had just over 4096 objects on it?

With this patch, a slab with 5000 objects on it will
get 1 item scanned, while a slab with 4000 objects on
it will see shrinker->batch or SHRINK_BATCH objects
scanned every time.

I don't know if this would cause any issues, just
something to ponder.

If nobody things this is a problem, you can give the
patch my:

Acked-by: Rik van Riel <riel@surriel.com>

-- 
All Rights Reversed.

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