mm, mempolicy: rename slab_node for clarity

mm, mempolicy: rename slab_node for clarity

slab_node() is actually a mempolicy function, so rename it to
mempolicy_slab_node() to make it clearer that it used for processes with
mempolicies.

At the same time, cleanup its code by saving numa_mem_id() in a local
variable (since we require a node with memory, not just any node) and
remove an obsolete comment that assumes the mempolicy is actually passed
into the function.

Signed-off-by: David Rientjes <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Jianguo Wu <[email protected]>
Cc: Tim Hockin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>