Re: RFC: Non Power of 2 memory allocator

[Andi Kleen <ak@suse.de>]

Robin Getz <rgetz@blackfin.uclinux.org> writes:

> The  buddy system allocates things in power of 2 pages sizes (4k, 8k,
> 16k, 32k, 64k, 128k, 256k, 512k, 1024k), which works fine on most
> systems, but an embedded system, which is running without a MMU (
> Memory Management Unit) - RAM is precious, and when you only need
> 129k for an application, you don't want to allocate a power of 2,
> which gives you 256k -  an extra 127k, which can't be used by
> anything else.

In 2.4 I solved this problem at some point by just returning
the excess pages to the buddy allocator. There was even
a nice function to do this (alloc_exact)

That won't work for slab, but does for __get_free_pages() which
is better for large allocations anyways. slab imho doesn't make
sense for allocation anywhere bigger PAGE_SIZE/2. At some
point in 2.6 there was trouble with "compound pages" but I think
that has been resolved. 

Just implementing alloc_exact again would be the simplest solution
for your problem.

-Andi