Re: [patch 1/2] agpgart - allow user-populated memory types.

[Thomas Hellström <thomas@tungstengraphics.com>]

Arjan van de Ven wrote:
> On Tue, 2006-12-19 at 13:47 +0100, Thomas Hellström wrote:
>   
> > Arjan van de Ven wrote:
> >
> >     
> > > > A short background:
> > > > The current code uses vmalloc only. The potential use of kmalloc was 
> > > > introduced
> > > > to save memory and cpu-speed.
> > > > All agp drivers expect to see a single memory chunk, so I'm not sure we 
> > > > want to have an array of pages. That may require rewriting a lot of code.
> > > >    
> > > >
> > > >         
> > > but if it's clearly the right thing.....
> > > How hard can it be? there are what.. 5 or 6 AGP drivers in the kernel?
> > >
> > >
> > >  
> > >
> > >       
> > Hmm,
> > but we would still waste a lot of memory compared to kmalloc,
> >     
>
> surely it's at most 4Kb for the entire system?
>
>   
Nope. These structures get allocated once per display memory buffer, and 
a display memory buffer may be as large as
the AGP aperture size, (usually up to 512MB) or as small as one page.
The latter could be a user allocating a texture buffer for each 
character in a font, and they can be quite numerous, so we would waste 
almost 4Kb per buffer, which is not acceptable.

> (if agp allows the non-root user to pin a lot more than that in kernel
> memory there is a different problem of rlimits ;)
>
>   
The drm memory manager sets aside and keeps track of a preset amount of 
memory that can be pinned in the kernel for video use, which is shared 
by all users running direct rendering clients. Currently this is a hard 
limit, but the idea is to unlock memory and make it swappable if 
resources become scarce. The memory we're discussing above is included 
in the bookkeeping.

/Thomas



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