mm: memcontrol: expose THP events on a per-memcg basis

mm: memcontrol: expose THP events on a per-memcg basis

Currently THP allocation events data is fairly opaque, since you can
only get it system-wide.  This patch makes it easier to reason about
transparent hugepage behaviour on a per-memcg basis.

For anonymous THP-backed pages, we already have MEMCG_RSS_HUGE in v1,
which is used for v1's rss_huge [sic].  This is reused here as it's
fairly involved to untangle NR_ANON_THPS right now to make it per-memcg,
since right now some of this is delegated to rmap before we have any
memcg actually assigned to the page.  It's a good idea to rework that,
but let's leave untangling THP allocation for a future patch.

[[email protected]: fix build]
[[email protected]: fix memcontrol build when THP is disabled]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Chris Down <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Roman Gushchin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>