Video memory as swap under FreeBSD

[Warner Losh]

From: "Kevin - Your.Org" <kevin at your.org>
Subject: Re: Video memory as swap under FreeBSD
Date: Fri, 12 Oct 2007 11:54:23 -0500

> 
> On Oct 12, 2007, at 11:07 AM, Stefan Esser wrote:
> 
> > Vladimir Terziev schrieb:
> >> 	You're right,
> >>
> >> 	the swap, typically configured, is much more than the amount of  
> >> the video memory, but in fact the swap is just a reserv, which  
> >> ensures continuation of the normal operations on the machine, at  
> >> times of peak loads.
> >> 	In our days the amount of RAM placed in the servers is so much,  
> >> that the swap, in fact, is rarely used at all and a very small  
> >> amount of it (several MB) is used. In that cases having a very  
> >> fast swap space in the Video RAM, in addition to the disk swap,  
> >> would be a good solution.
> >
> > If you have a video card with so much excess memory, that you can  
> > use it
> > for swap, then I wonder whether the video card has not been much too
> > expensive ;-)
> >
> > How about spending $25 for another Gigabyte of RAM (real RAM, not  
> > SWAP)
> > instead?
> >
> 
> I'm not commenting on if this is a good idea or not either way, but  
> at least one vendor of servers that we've been buying from is now  
> including 128 or 256MB of video ram(not UMA, real video ram) embedded  
> on the motherboard now.
> 
> I thought it was odd too, until I asked our sales rep. The 8MB ATI  
> chipset they used to use would have disqualified them from being  
> "Vista Capable".
> 
> So, whether we want it or not, we're getting at least 128MB of video  
> memory on our servers now. I'd thought about trying to use it for  
> something, but decided it wasn't worth the effort. :)

It would be a cool hack.  it would also be cool technology to have
around because to 'swap' to the video ram, you need to have a way to
map it to a device.  And if you have that, then you have a short delta
to many of the pci based battery backed ram disks.

I'm sure that writing a small geom driver to cope wouldn't be very
hard to do.

Warner