On Tue, Feb 09, 2021 at 11:33:02AM -0500, Johannes Weiner [off-list ref] wrote:

Rstat combines the best of both worlds: from the write side, it
cheaply maintains a queue of cgroups that have pending changes, so
that the read side can do selective tree aggregation. This way the
reported stats will always be precise and recent as can be, while the
aggregation can skip over potentially large numbers of idle cgroups.

IIUC, on the unified hierarchy the rstat tree built from writer
notifications is shared with all controllers. (Currently, it means
memory updates are merged with base stats cpu time updates.) This is
just for reference, to stress the current rstat design.

---
 include/linux/memcontrol.h |  67 ++++++-----
 mm/memcontrol.c            | 223 +++++++++++++++----------------------
 2 files changed, 132 insertions(+), 158 deletions(-)

Well done.

Reviewed-by: Michal Koutný <mkoutny@suse.com>