swap_pager complaints but not using swap

[Dieter]

> > AMD64  FreeBSD 7.0  2 GiB main memory
> > 
> > My console says:
> > 
> > login: swap_pager: indefinite wait buffer: bufobj: 0, blkno: 22, size: 4096
> > swap_pager: indefinite wait buffer: bufobj: 0, blkno: 22, size: 4096
> > swap_pager: indefinite wait buffer: bufobj: 0, blkno: 22, size: 4096
> > swap_pager: indefinite wait buffer: bufobj: 0, blkno: 22, size: 4096
> > 
> > pstat -sk
> > Device          1K-blocks     Used    Avail Capacity
> > /dev/ad6s10       4590208       96  4590112     0%
> > 
> > Wow, using a whole 96K of swap.  I don't see any disk related
> > complaints in dmesg.
> > 
> > Is this something to worry about?
> 
> Yes, the system was *trying* to do swap I/O and timing out while doing so.
> 
> Kris

Whoops, I forgot to change the subject line after adding the k option
to pstat.  Without the k it said 0 used.  And this morning it occurs to
me that even if swap used was zero, it could have been trying to *start*
using swap.

Anyway... given this timeout explaination, I'm guessing that page/swap
has to compete with user processes for disk i/o, and thus probably
suffers from the same lack of fair i/o scheduling that user processes
suffer from.  E.g. one process doing disk i/o can lock out another
process for at least several minutes, probably indefinitely.  :-(