Subject: Re: Limiting disk I/O?
To: Tech-kern <>
From: Jukka Marin <>
List: tech-kern
Date: 11/12/2007 15:25:51
On Mon, Nov 12, 2007 at 01:48:58PM +0100, Joerg Sonnenberger wrote:
> Look for BUFQ_PRIOCSCAN and BUFQ_READPRIO in GENERIC. They are not
> enabled by default. kern.bufq.strategies lists the available strategies.


kern.bufq.strategies = disksort fcfs

> > # dkctl ld1 strategy
> > dkctl: /dev/rld1d: DIOCGSTRATEGY: Inappropriate ioctl for device
> I don't know whether a driver has to do anything to get this, others can
> comment on that I guess.

I hope ;-)

> > Softdep is a big win most of the time.  Disabling it "fixes" the problem I
> > described, but it also makes all disk I/O much slower.
> It might help to modify vfs.sync in that case to force softdep to be
> less aggressive. It can also help to increate kern.maxvnodes.

Where are the vfs.sync variables documented?  I think I tried to increase
kern.maxvnodes and it made things worse (or so it seemed).