Re: [PATCH] mm/slub: improve count_partial() for CONFIG_SLUB_CPU_PARTIAL

From: Christopher Lameter
Date: Sun Feb 23 2020 - 20:29:12 EST

On Sat, 22 Feb 2020, Wen Yang wrote:

> We also observed that in this scenario, CONFIG_SLUB_CPU_PARTIAL is turned
> on by default, and count_partial() is useless because the returned number
> is far from the reality.

Well its not useless. Its just not counting the partial objects in per cpu
partial slabs. Those are counted by a different counter it.

> Therefore, we can simply return 0, then nr_free is also 0, and eventually
> active_objects == total_objects. We do not introduce any regression, and
> it's preferable to show the unrealistic uniform 100% slab utilization
> rather than some very high but incorrect value.

I suggest that you simply use the number of partial slabs and multiply
them by the number of objects in a slab and use that as a value. Both
values are readily available via /sys/kernel/slab/<...>/

You dont need a patch to do that.