Re: [PATCH] i386: single node SPARSEMEM fix

[Magnus Damm <magnus.damm@gmail.com>]

On 9/8/05, Dave Hansen <haveblue@us.ibm.com> wrote:
> On Tue, 2005-09-06 at 12:56 +0900, Magnus Damm wrote:
> > This patch for 2.6.13-git5 fixes single node sparsemem support. In the case
> > when multiple nodes are used, setup_memory() in arch/i386/mm/discontig.c calls
> > get_memcfg_numa() which calls memory_present(). The single node case with
> > setup_memory() in arch/i386/kernel/setup.c does not call memory_present()
> > without this patch, which breaks single node support.
> 
> First of all, this is really a feature addition, not a bug fix. :)

>From the POV that you can use sparsemem on a PC, yes. But from the POV
that setup_memory() in arch/i386/kernel/setup.c not includes a call to
memory_present(), I think it is a fix. =)

While at it, why do we have two copies of setup_memory()? Couldn't
NUMA and non-NUMA share the same code? OTOH, NUMA and discontigmem
seems very integrated/mixed up and there seems to be much activity in
this field so maybe it is nice to keep the NUMA part separated anyway.
 
> The reason we haven't included this so far is that we don't really have
> any machines that need sparsemem on i386 that aren't NUMA.  So, we
> disabled it for now, and probably need to decide first why we need it
> before a patch like that goes in.

Well, I do not have any hardware here that requires sparsemem either,
but I wanted to add NUMA emulation code to be able to run some
multiple-memory-nodes tests on a virtual PC in QEMU. And this little
patch shows my first step which involved getting sparsememto run on a
PC.

> I actually have exactly the same patch that you sent out in my tree, but
> it's just for testing.  Magnus, perhaps we can get some of my testing
> patches in good enough shape to put them in -mm so that the non-NUMA
> folks can do more sparsemem testing.

Well, my NUMA emulation project has been postponed a bit now, but
sooner or later I or someone else will need sparsemem on non-NUMA. So
getting your testing patches in to -mm seems like a good idea!

Thanks!

/ magnus
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