sched, numa, mm: Introduce tsk_home_node()

sched, numa, mm: Introduce tsk_home_node()

Introduce the home-node concept for tasks. In order to keep memory
locality we need to have a something to stay local to, we define the
home-node of a task as the node we prefer to allocate memory from and
prefer to execute on.

These are no hard guarantees, merely soft preferences. This allows for
optimal resource usage, we can run a task away from the home-node, the
remote memory hit -- while expensive -- is less expensive than not
running at all, or very little, due to severe cpu overload.

Similarly, we can allocate memory from another node if our home-node
is depleted, again, some memory is better than no memory.

This patch merely introduces the basic infrastructure, all policy
comes later.

NOTE: we introduce the concept of EMBEDDED_NUMA, these are
architectures where the memory access cost doesn't depend on the cpu
but purely on the physical address -- embedded boards with cheap
(slow) and expensive (fast) memory banks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-ii8j8cp87cgctecfqp2ib6rn@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>