Allocalting > 4M

Allocalting > 4M

[Rune Torgersen]

We have an embedded board with 1G of memory.

Is there any way, short of using mem=3D on kernel command line and
reserving memory, to allocate more than 4M of contigous physical memory?
We're trying to allocalte a 8M buffer for use in some DMA transfers for
a bank of DSP's.
We were using get_Free_pages to allocate the meory before we made the
buffer bigger. It seems that get_free_pages cannot allocate more than
2^10 pages (4M on ppc)
I also tried alloc_bootmem, but it fails also.

Re: Allocalting > 4M

[Roger Larsson]

On Wednesday 27 September 2006 22:34, Rune Torgersen wrote:
> We have an embedded board with 1G of memory.
>
> Is there any way, short of using mem= on kernel command line and
> reserving memory, to allocate more than 4M of contigous physical memory?
> We're trying to allocalte a 8M buffer for use in some DMA transfers for
> a bank of DSP's.
> We were using get_Free_pages to allocate the meory before we made the
> buffer bigger. It seems that get_free_pages cannot allocate more than
> 2^10 pages (4M on ppc)
> I also tried alloc_bootmem, but it fails also.

There is a 'bigphysmem' patch for 2.4 that might help. There might be
alternative solutions to this problem, they should refere to bigphysmem
- might help when googling...

/RogerL

Re: Allocalting > 4M

[Arnd Bergmann]

Am Wednesday 27 September 2006 22:34 schrieb Rune Torgersen:
> Is there any way, short of using mem= on kernel command line and
> reserving memory, to allocate more than 4M of contigous physical memory?
> We're trying to allocalte a 8M buffer for use in some DMA transfers for
> a bank of DSP's.
> We were using get_Free_pages to allocate the meory before we made the
> buffer bigger. It seems that get_free_pages cannot allocate more than
> 2^10 pages (4M on ppc)
> I also tried alloc_bootmem, but it fails also.

alloc_bootmem is supposed to handle this case, but you can only call
that very early in your code, before the buddy allocator kicks in
(free_all_bootmem()). Maybe you should just check why it fails for you.

	Arnd <><

RE: Allocalting > 4M

[Rune Torgersen]

=20

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@arndb.de]=20
> alloc_bootmem is supposed to handle this case, but you can only call
> that very early in your code, before the buddy allocator kicks in
> (free_all_bootmem()). Maybe you should just check why it=20
> fails for you.

I was calling it in the wrong board init function.=20
m82xx_board_init was too early, and our platform_init was too late.

It works now.