Re: Dirty Buffer Writing [was Proposed LogWriter Scheme]

> Greg Copeland <greg@CopelandConsulting.Net> writes:
> > Doesn't this also increase the likelihood that people will be
> > running in a buffer-poor environment more frequently that I
> > previously asserted, especially in very heavily I/O bound
> > systems?  Unless I'm mistaken, that opens the door for a
> > general case of why an aio implementation should be looked into.

Neil Conway replies:
> Well, at least for *this specific sitation*, it doesn't really change
> anything -- since FreeBSD doesn't implement POSIX AIO as far as I
> know, we can't use that as an alternative.

I haven't tried it yet but there does seem to be an aio implementation that
conforms to POSIX in FreeBSD 4.6.2.  Its part of the kernel and can be
found in:
/usr/src/sys/kern/vfs_aio.c

> However, I'd suspect that the FreeBSD kernel allows for some way to
> tune the behavior of the syncer. If that's the case, we could do some
> research into what settings are more appropriate for FreeBSD, and
> recommend those in the docs. I don't run FreeBSD, however -- would
> someone like to volunteer to take a look at this?

I didn't see anything obvious in the docs but I still believe there's some
way to tune it. I'll let everyone know if I find some better settings.

> BTW Curtis, did you happen to check whether this behavior has been
> changed in FreeBSD 5.0?

I haven't checked but I will.