Re: [PATCH] IA64: Sparse and Discontig Mem need NUMA

[Simon Horman <horms@verge.net.au>]

On Wed, May 02, 2007 at 09:22:58AM -0700, Luck, Tony wrote:
> > This seems line an issue best solved by prohibiting such settings through
> > Kconfig. But if it is desirable for sparse and discontig memory to work
> > without CONFIG_NUMA let me know and I'll have a stab at it. It does seem
> > possible code-wise. I'm just not sure if its useful.
> 
> I pretty sure that we used to be able to build for a DISCONTIG but
> non-NUMA system ... this is a quite common case, systems with >4G
> of memory put the first 2G at 0-2G, reserve the 2G-4G area for
> PCI memory mapped devices (and other platform specific stuff) then
> the rest of RAM is at some >4G address.  With just a 2G hole it
> is possible to paper over it, but some systems put the extra
> memory at much higher addresses.

I did take a look at what it would take to allow Sparse to compile
in non-NUMA. It seemed that Sparse was very much centered around NUMA
so I wondered how useful the result might be. I will take a look
into Discontig and see what is required there.

> But it would be nice to reduce the CONFIG maze ... so perhaps we
> should ponder what overhead such a system would suffer by having
> to be built as CONFIG_NUMA=y.  If this is small, then perhaps we
> can simplify things.

I guess it might be a bit tricky to measure that comprehensively.
But it would certainly make things easier. I think that the patch
I sent implements what you are suggesting, though perhaps it isn't
exactly what you had in mind.

-- 
Horms
  H: http://www.vergenet.net/~horms/
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