Re: [PATCH v2] Fix fake numa on ppc

On Wed, 2 Sep 2009, Ankita Garg wrote:

Hi,

Below is a patch to fix a couple of issues with fake numa node creation
on ppc:

1) Presently, fake nodes could be created such that real numa node
boundaries are not respected. So a node could have lmbs that belong to
different real nodes.

On x86_64, we can use numa=off to completely disable NUMA so that all 
memory and all cpus are mapped to a single node 0.  That's an extreme 
example of the above and is totally permissible.

2) The cpu association is broken. On a JS22 blade for example, which is
a 2-node numa machine, I get the following:

# cat /proc/cmdline
root=/dev/sda6  numa=fake=2G,4G,,6G,8G,10G,12G,14G,16G
# cat /sys/devices/system/node/node0/cpulist
0-3
# cat /sys/devices/system/node/node1/cpulist
4-7
# cat /sys/devices/system/node/node4/cpulist

#

This doesn't show what the true NUMA topology of the machine is, could you 
please post the output of

	$ cat /sys/devices/system/node/node*/cpulist
	$ cat /sys/devices/system/node/node*/distance
	$ ls -d /sys/devices/system/node/node*/cpu[0-8]

from a normal boot without any numa=fake?

So, though the cpus 4-7 should have been associated with node4, they
still belong to node1. The patch works by recording a real numa node
boundary and incrementing the fake node count. At the same time, a
mapping is stored from the real numa node to the first fake node that
gets created on it.

If there are multiple fake nodes on a real physical node, all cpus in that 
node should appear in the cpulist for each fake node for which it has 
local distance.