memcg: sleep during flushing stats in safe contexts

Currently, all contexts that flush memcg stats do so with sleeping not
allowed.  Some of these contexts are perfectly safe to sleep in, such as
reading cgroup files from userspace or the background periodic flusher. 
Flushing is an expensive operation that scales with the number of cpus and
the number of cgroups in the system, so avoid doing it atomically where
possible.

Refactor the code to make mem_cgroup_flush_stats() non-atomic (aka
sleepable), and provide a separate atomic version.  The atomic version is
used in reclaim, refault, writeback, and in mem_cgroup_usage().  All other
code paths are left to use the non-atomic version.  This includes
callbacks for userspace reads and the periodic flusher.

Since refault is the only caller of mem_cgroup_flush_stats_ratelimited(),
change it to mem_cgroup_flush_stats_atomic_ratelimited().  Reclaim and
refault code paths are modified to do non-atomic flushing in separate
later patches -- so it will eventually be changed back to
mem_cgroup_flush_stats_ratelimited().

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yosry Ahmed <[email protected]>
Acked-by: Shakeel Butt <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Michal Koutný <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Vasily Averin <[email protected]>
Cc: Zefan Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions