Re: [PATCH v2] memcg: add tracing for memcg stat updates

[Johannes Weiner]

On Tue, Oct 15, 2024 at 02:37:21PM -0700, Shakeel Butt wrote:
> 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.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Cc: JP Kobryn <inwardvessel@xxxxxxxxx>
> Cc: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>