Re: [Lhms-devel] Re: 150 nonlinear

[Dave Hansen <haveblue@us.ibm.com>]

On Tue, 2004-10-26 at 14:20, Mika Penttila wrote:
> "There are two problems that are being solved: having a sparse layout
> requiring splitting up mem_map (solved by discontigmem and your
> nonlinear), and supporting non-linear phys to virt relationships (Dave
> M's implentation which does the mem_map split as well)."
> 
> 
> so what's the split?

So, mem_map is normally laid out so that, if you have 1GB of memory, the
memory for 0x00000000 is at mem_map[0], and the memory for the last page
(at 1GB - 1 page) is at mem_map[1<<30 / PAGE_SIZE - 1].  

That's fine and dandy for most systems.  But, imagine that you have some
memory on a funky machine where you have 2GB of memory, but it is laid
out like this:

    0-1 GB - first 1 GB
  1-100 GB - empty
100-101 GB - second 1 GB

Then, you'd need to have mem_map sized the same as a 101GB system on
your dinky 2GB system (disregard the ia64 implementation).

The split I'm referring to is cutting mem_map[] up into pieces for each
contiguous section of memory.  

Make sense?

-- Dave

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