sched/numa: Avoid migrating tasks that are placed on their preferred node

This patch classifies scheduler domains and runqueues into types depending
the number of tasks that are about their NUMA placement and the number
that are currently running on their preferred node. The types are

regular: There are tasks running that do not care about their NUMA
	placement.

remote: There are tasks running that care about their placement but are
	currently running on a node remote to their ideal placement

all: No distinction

To implement this the patch tracks the number of tasks that are optimally
NUMA placed (rq->nr_preferred_running) and the number of tasks running
that care about their placement (nr_numa_running). The load balancer
uses this information to avoid migrating idea placed NUMA tasks as long
as better options for load balancing exists. For example, it will not
consider balancing between a group whose tasks are all perfectly placed
and a group with remote tasks.

Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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