Subject: Re: proper way to reserve a chunk of memory at the top of the kernel?

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 20 Jul 2009 11:54:05 +1000

On Tue, 2009-07-14 at 15:18 -0600, Chris Friesen wrote:
> I have a powerpc board with 512BM of memory.  The BIOS has a chunk of
> memory at the top end of physical memory which it does not zero out over
> a reboot.
> 
> What's the proper way to tell linux that this chunk of physical memory
> should be ignored (so that we can access it later without worrying that
> Linux will try to allocate it)?  Should I be calling
> 
> lmb_reserve(lmb_end_of_DRAM() - size, size);
> 
> in early_reserve_mem() or is there a better mechanism?

The device-tree blob contains a special "reserve map" in the header,
which automatically turns into calls to lmb_reserve() early during boot,
so putting your special region in that map should be the right way to do
what you want without special code.

> For comparison, in an older kernel this was done in set_phys_avail(), by
> calling mem_pieces_remove(&phys_avail, total_lowmem - size, size, 1);

Cheers,
Ben.

> Thanks,
> 
> Chris
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