Re: [patch] 4GB I/O, cut three

[Andrea Arcangeli]

[ my usual email is offline at the moment, please CC to [e-mail]
  for anything urgent until the problem is fixed ]

On Wed, May 30, 2001 at 11:55:38AM +0200, Jens Axboe wrote:
> On Wed, May 30 2001, Mark Hemment wrote:
> > Hi Jens,
> > 
> >   I ran this (well, cut-two) on a 4-way box with 4GB of memory and a
> > modified qlogic fibre channel driver with 32disks hanging off it, without
> > any problems.  The test used was SpecFS 2.0
> 
> Cool, could you send me the qlogic diff? It's the one-liner can_dma32
> chance I'm interested in, I'm just not sure what driver you used :-)
> I'll add that to the patch then. Basically all the PCI cards should
> work, I'm just being cautious and only enabling highmem I/O to the ones
> that have been tested.
> 
> >   Peformance is definitely up - but I can't give an exact number, as the
> > run with this patch was compiled with no-omit-frame-pointer for debugging
> > any probs.
> 
> Good
> 
> >   I did change the patch so that bounce-pages always come from the NORMAL
> > zone, hence the ZONE_DMA32 zone isn't needed.  I avoided the new zone, as
> > I'm not 100% sure the VM is capable of keeping the zones it already has
> > balanced - and adding another one might break the camels back.  But as the
> > test box has 4GB, it wasn't bouncing anyway.
> 
> You are right, this is definitely something that needs checking. I
> really want this to work though. Rik, Andrea? Will the balancing handle
> the extra zone?

The bounces can came from the ZONE_NORMAL without problems, however the
ZONE_DMA32 way is fine too, but yes probably it isn't needed in real
life unless you do an huge amount of I/O at the same time. If you want
to reduce the amount of changes you can defer the zone_dma32 patch and
possibly plug it in later.

Andrea