how can I cleanly exclude memory from the kernel memory allocator?

On 24 Mar 11 19:27, Nicolas Pitre wrote:

On Thu, 24 Mar 2011, Larry Bassel wrote:

quoted

I want to (early in system initialization) exclude some
contiguous physical memory from one or more memory banks
so that it won't be mapped in the normal kernel 1-to-1 mapping
(so that it can be mapped uncached, strongly ordered, etc.
as needed -- I know that it is forbidden to have a cached
and an uncached mapping to the same memory) and so that it
won't be freed into the kernel memory allocator (so that
it won't fragment and can be allocated using genalloc).

I have tried to find a clean way to do this, but none of
the approaches I've considered seem very good:

1. Add a hook to the memory tag parsing routine to (possibly)
change each tag before arm_add_memory() is called,
or alter arm_add_memory() itself.

There is already a hook for that.  In your machine descriptor you can 
add a .fixup method to do just that.  See tag_fixup_mem32() in 
arch/arm/mach-orion5x/common.c for a usage example.

I thought fixup was called before the tags were parsed so
that one could (for instance) set up a memory configuration
which would override the tags (such as what is done in 
arch/arm/mach-msm/board-halibut,c) -- while I could presumably
parse the tags myself there to get the memory map
that the bootloader passed in (and alter it), this seems like
a duplication of effort.

Nicolas

Larry

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