Re: SLUB ia64 linux-next crash bisected to 756dee75

[Alex Chiang <achiang@hp.com>]

* Christoph Lameter <cl@linux-foundation.org>:
> On Wed, 13 Jan 2010, Alex Chiang wrote:
> 
> > Firmware puts each cell into a NUMA node, so we should really
> > only have 2 nodes, but for some reason, that 3rd node gets
> > created too. I haven't inspected the SRAT/SLIT on this machine
> > recently, but can do so if you want me to.
> 
> May not have anything to do with the problem we are looking at but memory
> setup is screwed up. Funky effects may follow.

Actually, I was reminded off-list by my HP colleagues that the
memory setup I showed you is common on mid-range and high-end HP
ia64 platforms.

Lee tells me:

	The third node is the "interleaved memory" pseudo-node.
	The firmware always interleaves 512MB of phys address
	space across the nodes.  On these platforms, only
	interleaved memory is at phys addr 0--needed by firmware,
	...  All the real NUMA nodes' memory starts at some high
	phys addr. So, even in "numa mode" [a.k.a. 100% cell
	local memory], the firmware must create a region of
	interleaved memory at phys 0.  So, we get N+1 nodes.

	Because node 2 is at phys 0 and contains only 512MB, it
	is all ZONE_DMA memory.  DMA zone is 1st 4G on ia64.

Our platforms have been shipping like this for years, so it's not
like anything recent has changed.

Thanks,
/ac

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