RE: [Dri-devel] agp: what if memory is fragmented?

[Alexander S. <Ale...@at...>]

The GART is the paging unit of the AGP system.

It deals nicely with fragmented chunks of page sized
memory chunks. So you only need some sort of memory
allocation and a way to determine eachs pages physical
adress to use it for those GART purposes.

You just need to ensure that your memory is permanent,
which means its neither moved around in physical memory
nor swapped to harddisk. And you can have some 2GB gart
range whilst you only have a few 100 MB real physical
ram in your machine. The idea is to provide as much 
linearly rearanged memory space so that all your one or 
two gart clients do have enough linear space to remap to.

Regards Alex.

> -----Original Message-----
> From: Philip Brown [mailto:ph...@bo...]
> Sent: Saturday, December 22, 2001 01:06
> To: dri...@li...
> Subject: [Dri-devel] agp: what if memory is fragmented?
> 
> 
> Sorry if this is repeat: haven't seen my original show up in 12 hours.
> 
> I have a question about "what if physical memory is fragmented"?
> The AGIPIOC_ALLOC call returns a 'physical' address.
> This implies that the ALLOC is a single contiguous chunk of physical
> memory. Right?
> 
> However, I cant imagine that it is easy to guarantee 64 megs 
> of contiguous
> physical RAM allocation. So something seems wrong with my assumption.
> 
> 
> I've looked at the bsd AGP source, and it uses "malloc()", 
> and some fancy
> bsd magic that I dont understand.
> Similarly, I do not understand the linux page allocation stuff at all.
> 
> 
> So, what should be the behaviour of my agp implementation, if 
> contiguous
> physical memory is not available?
> I would think it should not be neccessary: thats why the GATT 
> exists, after
> all?!
> 
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