Disk cache causing swap usage

[Doug White]

On Tue, 14 Jun 2005, Brian Rogers wrote:

> I have 1 GB of RAM and a 2 GB swap partition.  Previously, I would
> almost never see swap used (or at least no more than 4k used) under
> normal use, but that appears to have changed recently.
>
> I am running
> FreeBSD 6.0-CURRENT #3: Tue Jun 14 14:25:20 PDT 2005
> root at brian:/usr/obj/usr/src/sys/MYKERN
>
> My testcase for this problem is to run
> dd if=bigfile of=/dev/null
> and watch the free space drop.  I expect that to happen, as the disk
> cache holds onto what has been read.  But when free memory runs out, it
> starts paging out to the swap file, when it should have plenty of old
> cache to throw out first before resorting to the swap file.  I'm pretty
> sure it didn't do this before, but I ran into the 20050609 issue in
> UPDATING when trying to run top on an old kernel to test it.

This is a known bug in the bufcache work. phk is aware but an extra prod
wouldn't hurt :)

-- 
Doug White                    |  FreeBSD: The Power to Serve
dwhite at gumbysoft.com          |  www.FreeBSD.org