mm: memcontrol: optimize per-lruvec stats counter memory usage

mm: memcontrol: optimize per-lruvec stats counter memory usage

The vmstat threshold is 32 (MEMCG_CHARGE_BATCH), Actually the threshold
can be as big as MEMCG_CHARGE_BATCH * PAGE_SIZE.  It still fits into s32.
So introduce struct batched_lruvec_stat to optimize memory usage.

The size of struct lruvec_stat is 304 bytes on 64 bit systems.  As it is a
per-cpu structure.  So with this patch, we can save 304 / 2 * ncpu bytes
per-memcg per-node where ncpu is the number of the possible CPU.  If there
are c memory cgroup (include dying cgroup) and n NUMA node in the system.
Finally, we can save (152 * ncpu * c * n) bytes.

[[email protected]: fix typo in comment]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Muchun Song <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: Chris Down <[email protected]>
Cc: Yafang Shao <[email protected]>
Cc: Wei Yang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>