vmalloc limits in PPC kernels ?

[vinai]

Matt,

Thanks much for the information you provided below.  Are there any
pointers/references as to why these changes were actually implemented,
or is it really a case of "the source being the guide" ?  As I said,
this issue is really troubling for us, and I want to see if there is
a "clean" way to circumvent that limit without screwing up the MM
subsystem (at least not too badly :) ...

cheers
vinai

On Thu, 13 Feb 2003, Matt Porter wrote:

> All architectures have a limit.  Its size is defined by
> VMALLOC_END-VMALLOC_START and further limited by the size of each
> preceding allocation (+ a PAGE_SIZE pad) before the allocation in
> question.  Allocations also include ioremaps and on some architectures
> consistent memory allocations absorb vmalloc space.
>
> You can see the constraints in asm-ppc/pgtable.h.  On PPC, it is possible
> to change the default parameters in order to expand the amount of vmalloc
> space available.  This is accomplished via config options under the
> advanced kernel options menu.  With PAGE_OFFSET at 0x40000000 and highmem,
> I've run a system with nearly 3GB of vmalloc space.

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