[Lhms-devel] Re: Help text for memory model config section?

[Anton Blanchard]

Hi,

> It's not a big deal to go and free up the bits of that which we don't
> use, especially if there's not going to be any memory hotplug going on.

Yep, we have tried to keep the bloat of the generic kernel with NUMA
down so its acceptable to a G5 user. It would be nice to only allocate
that 256kB when required.

Seeing that sparsemem and the ppc64 NUMA code keep a similar structure
indexed by address, does it make sense to consolidate that and keep the
numa lookup info in the sparsemem structure?

> However, if you want memory hotplug, I think 256k at boot-time in .bss
> is a pretty small price to pay if it gets you up anywhere from 256MB to
> 2TB of memory.

I tested sparsemem for the 16TB case:

 #define SECTION_SIZE_BITS       24
-#define MAX_PHYSADDR_BITS       38
-#define MAX_PHYSMEM_BITS        36
+#define MAX_PHYSADDR_BITS       44
+#define MAX_PHYSMEM_BITS        44

   text    data     bss     dec     hex  filename
5337004 3017328  579744  8934076  8852bc 1/vmlinux
5337032 3017328 8935584 17289944 107d2d8 2/vmlinux

So bumping the bits from 38 to 44 increased the kernel to ~17MB. 

Anton