Re: [patch 2/4] add x86-64 Kconfig options for sparsemem

[Andi Kleen <ak@muc.de>]

On Wed, May 18, 2005 at 09:43:48AM -0700, Matt Tolentino wrote:
> >From: Andi Kleen <ak@muc.de>
> >On Wed, May 18, 2005 at 08:24:41AM -0700, Matt Tolentino wrote:
> >> 
> >> Add the requisite arch specific Kconfig options to enable 
> >> the use of the sparsemem implementation for NUMA kernels
> >> on x86-64.
> >
> >How much did you test sparsemem on x86-64 NUMA ? 
> >
> >There are various cases that probably need to be checked,
> >AMD with SRAT, AMD without SRAT, AMD with more than 4GB RAM, 
> >Summit(?), NUMA EMULATION etc.
> >
> >If all that works I would have no problem with removing the
> >old code.
> 
> As my disclaimer said, this has only been tested using
> the NUMA EMULATION config option.  That's a big part of
> the reason for sending this out  - to get further testing 
> on real x86-64 NUMA systems, but without breaking the
> current discontigmem code.  

Hmm, I would have assumed IBM tested it, since Dave Hansen signed off - 
they have a range of Opteron machines.   If not I can test it
on a few boxes later.

A single box is not enough, there are various special cases. 
e.g. one area I've been fighting with is that
with SRAT and 3+GB memory the nodes don't span the PCI memory
hole anymore, and when there is a virt_to_page() or similar for these
addresses things go wrong because they do a uninitialized hash
table lookup. If it's not that hard and doesn't cause code bloat
I would recommend to harden sparsemem against this case, at least for 
upto 4GB.

-Andi