Allocating non-contigious memory

Allocating non-contigious memory

[Olivier Galibert]

What is the Right Way[tm] as of 2.4.6 to allocate 16Mb as 4K pages and
get the pci bus address for each page?  Bonus points is they're
virtually contiguous, but that's not necessary.  IIRC, the old
vmalloc-then-walk-the-pagetables trick is considered out-of-bounds
nowadays.

  OG.

Re: Allocating non-contigious memory

[Alan Cox]

> What is the Right Way[tm] as of 2.4.6 to allocate 16Mb as 4K pages and
> get the pci bus address for each page?  Bonus points is they're
> virtually contiguous, but that's not necessary.  IIRC, the old
> vmalloc-then-walk-the-pagetables trick is considered out-of-bounds
> nowadays.

If you want it virtually contiguous then copy the code from bttv that 
out-of-bounds or otherwise is now found in about 8 drivers in the kernel.

If you don't need that then you can map user space and use kiovecs - which
is nicer for many things

Re: Allocating non-contigious memory

[Riley Williams]

Hi Alan.

 >> What is the Right Way[tm] as of 2.4.6 to allocate 16Mb as 4K
 >> pages and get the pci bus address for each page?  Bonus points
 >> is they're virtually contiguous, but that's not necessary.
 >> IIRC, the old vmalloc-then-walk-the-pagetables trick is
 >> considered out-of-bounds nowadays.

 > If you want it virtually contiguous then copy the code from bttv
 > that out-of-bounds or otherwise is now found in about 8 drivers
 > in the kernel.

Would it be useful to turn that particular code into a subroutine that
is called from each driver, or would that cause other problems?

Best wishes from Riley.

Re: Allocating non-contigious memory

[Alan Cox]

> Would it be useful to turn that particular code into a subroutine that
> is called from each driver, or would that cause other problems?

It would but then I suspect Linus wouldnt want to take it as it might
encourage people to use it 8)