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

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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,
when the amount of memory needed is much less than one page, which tends to be
a very common case.

Unless we allow the first entry in the array to be the virtual adress to an
arbitrary-sized (max one page) kmalloc() area, the rest of the entries can be pointers
to pages allocated with __get_free_page().

This would almost introduce the same level of confusion as the original proposal, and effectively we'd be doing virtual address translation in software for each access.

If it's acceptable I'd like to go for the vmalloc / kmalloc flag, or at worst keep the current vmalloc only but that's such a _huge_ memory waste for small buffers. The flag was the original idea, but unfortunately the agp_memory struct is part of the drm interface, and I wasn't sure we could add a variable to it.

I doubt this is part of the userspace interface so for sure we can
change it to be right.


/Thomas

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