Commit r345200 (new ARC reclamation threads) looks suspicious to me - second potential problem

[Slawa Olhovchenkov]

On Wed, May 22, 2019 at 12:07:29PM -0400, Alexander Motin wrote:

> On 22.05.2019 11:50, Lev Serebryakov wrote:
> > On 22.05.2019 18:19, Alexander Motin wrote:
> > 
> >>>>  But looks like `arc_kmem_reap_soon()` is synchronous on FreeBSD! So,
> >>>> this `delay()` looks very wrong. Am I right?
> >>
> >> Why is it wrong?
> >  One second pause after synchronous operation to wait it completion?
> 
> No.  To rate-throttle them.  This gives UMA a second to get back into
> minimally steady state after we ripped all caches from it.  As I have
> told, we do not want to drain caches constantly in a tight loop, we want
> more or less steady state.

And also (posible) additionaly delay arc_get_data_impl().
This is incorrectly throttling implementation.