pageout question

[RW]

On Sun, 25 Jul 2010 17:19:41 +0300
Andriy Gapon <avg at freebsd.org> wrote:

> on 25/07/2010 16:41 RW said the following:

> > In FreeBSD the inactive queue contains disk cache pages which
> > normally provide most of the clean pages needed. In addition pages
> > are dribbled out to swap, and the resulting clean pages are placed
> > at the back of the inactive queue to make another pass. 
> 
> Well, "normally" and "most" are not quite quantitative.
> Personally, I do not see any guarantees that inactive queue would
> contain enough clean pages to reach paging target on a single pass.

I didn't say it say it was guaranteed. I just think the scenario where
a first pass ends up between the watermarks is rare. And when it
happens I don't see a compelling reason to do extra paging to reach an
arbitrary target.

I think the comment about not clearing vm_pages_needed is referring to
clearing it below the low-watermark because the daemon would then get
woken-up almost immediately.

> I meant bare minimum to stop paging, that is, going above lower
> watermark of the paging hysteresis.