[RFC PATCH 0/4] Improve slab consumption with memoryless nodes

[Nishanth Aravamudan <nacc@linux.vnet.ibm.com>]

Anton noticed (http://www.spinics.net/lists/linux-mm/msg67489.html) that
on ppc LPARs with memoryless nodes, a large amount of memory was
consumed by slabs and was marked unreclaimable. He tracked it down to
slab deactivations in the SLUB core when we allocate remotely, leading
to poor efficiency always when memoryless nodes are present.

After much discussion, Joonsoo provided a few patches that help
significantly. They don't resolve the problem altogether:

 - memory hotplug still needs testing, that is when a memoryless node
   becomes memory-ful, we want to dtrt
 - there are other reasons for going off-node than memoryless nodes,
   e.g., fully exhausted local nodes

Neither case is resolved with this series, but I don't think that should
block their acceptance, as they can be explored/resolved with follow-on
patches.

The series consists of:

[1/4] topology: add support for node_to_mem_node() to determine the fallback node
[2/4] slub: fallback to node_to_mem_node() node if allocating on memoryless node

 - Joonsoo's patches to cache the nearest node with memory for each
   NUMA node

[3/4] Partial revert of 81c98869faa5 (""kthread: ensure locality of task_struct allocations")

 - At Tejun's request, keep the knowledge of memoryless node fallback to
   the allocator core.

[4/4] powerpc: reorder per-cpu NUMA information's initialization

 - Fix what appears to be a bug with when the NUMA topology information
   is stored in the powerpc initialization code.

 arch/powerpc/kernel/smp.c | 12 ++++++------
 arch/powerpc/mm/numa.c    | 13 ++++++++++---
 include/linux/topology.h  | 17 +++++++++++++++++
 kernel/kthread.c          |  2 +-
 mm/page_alloc.c           |  1 +
 mm/slub.c                 | 24 ++++++++++++++++++------
 6 files changed, 53 insertions(+), 16 deletions(-)