On Wed, Feb 20, 2019 at 06:27:07PM +1100, Dave Chinner wrote:
> freeable = 1
>
> ratio 4.15 priority 4.16 4.18 new
> 1:100 1 12 0 batch 1
> 1.32 1 9 0 batch 1
> 1:12 1 6 0 batch 1
> 1:6 1 3 0 batch 1
> 1:1 1 1 1 batch 1
> @@ -479,7 +479,16 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>
> total_scan = nr;
> if (shrinker->seeks) {
> - delta = freeable >> priority;
> + /*
> + * Use a small non-zero offset for delta so that if the scan
> + * priority is low we always accumulate some pressure on caches
> + * that have few freeable objects in them. This allows light
> + * memory pressure to turn over caches with few freeable objects
> + * slowly without the need for memory pressure priority to wind
> + * up to the point where (freeable >> priority) is non-zero.
> + */
> + delta = ilog2(freeable);
The idea makes sense to me, but log2 fails us when freeable is
1. fls() should work, though.
> + delta += freeable >> priority;
> delta *= 4;
> do_div(delta, shrinker->seeks);
> } else {
