MAXPHYS bump for FreeBSD 13

[Konstantin Belousov]

On Sat, Nov 14, 2020 at 06:40:44PM -0500, Alexander Motin wrote:
> On 14.11.2020 13:37, Konstantin Belousov wrote:
> > On Sat, Nov 14, 2020 at 10:01:05AM -0500, Alexander Motin wrote:
> > 4. My larger concern is, in fact, cam and drivers.
> 
> I am actually the least concerned about this part.  I've already
> reviewed/cleaned it once, and can do again if needed.  We have some
> drivers unaware about MAXPHYS, and they should safely be limited to
> DFLTPHYS, the others should properly adapt.  And if you like to make
> MAXPHYS tunable -- I'd be happy to take this part.
Well, I looked at ahci(4) as a first driver, and it is already problematic.
It sizes internal structures, which are really some hardware command
structures, based on MAXPHYS.  Same for siis(4), but this seems to be even
worse due to +1.

> 
> >> Could you or somebody help with vfs/ffs code, where I suppose the
> >> smaller page lists are used?
> > Do you plan to work on this ?  I can help, sure.
> 
> Honestly, I haven't planned it.  But if that is a price to finally close
> this topic forever, I could probably figure out something.  Otherwise I
> was mostly looking for somebody to take this part of the project into
> capable hands.
> 
> > Still, I wanted to make MAXPHYS (and 'small' MAXPHYS, this is not same as
> > DFLPHYS), a tunable, in the scope of this work.
> 
> +1
I posted my WIP at https://reviews.freebsd.org/D27225.
It survived some limited testing, as described in comment.

Alexander, I will quite appreciate advise about changes I made to
dev/ahci and dev/siis.  Also I would be glad to receive patches for any
of the unhandled drivers, although I plan to do the pass over all of them
if nobody do that.

I did not assigned any reviewers, hopefully people would give same level
of interest to the review as to the discussion on the list.