memcg: add tracing for memcg stat updates

The memcg stats are maintained in rstat infrastructure which provides very
fast updates side and reasonable read side.  However memcg added plethora
of stats and made the read side, which is cgroup rstat flush, very slow. 
To solve that, threshold was added in the memcg stats read side i.e.  no
need to flush the stats if updates are within the threshold.

This threshold based improvement worked for sometime but more stats were
added to memcg and also the read codepath was getting triggered in the
performance sensitive paths which made threshold based ratelimiting
ineffective.  We need more visibility into the hot and cold stats i.e. 
stats with a lot of updates.  Let's add trace to get that visibility.

[[email protected]: use unsigned long type for memcg_rstat_events, per Yosry]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Shakeel Butt <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Reviewed-by: Yosry Ahmed <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Reviewed-by: T.J. Mercier <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: JP Kobryn <[email protected]>
Cc: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions