On Fri, May 08, 2020 at 10:06:30AM -0700, Shakeel Butt wrote: > One way to measure the efficiency of memory reclaim is to look at the > ratio (pgscan+pfrefill)/pgsteal. However at the moment these stats are > not updated consistently at the system level and the ratio of these are > not very meaningful. The pgsteal and pgscan are updated for only global > reclaim while pgrefill gets updated for global as well as cgroup > reclaim. > > Please note that this difference is only for system level vmstats. The > cgroup stats returned by memory.stat are actually consistent. The > cgroup's pgsteal contains number of reclaimed pages for global as well > as cgroup reclaim. So, one way to get the system level stats is to get > these stats from root's memory.stat, so, expose memory.stat for the root > cgroup. > > from Johannes Weiner: > There are subtle differences between /proc/vmstat and > memory.stat, and cgroup-aware code that wants to watch the full > hierarchy currently has to know about these intricacies and > translate semantics back and forth. > > Generally having the fully recursive memory.stat at the root > level could help a broader range of usecases. The changelog begs the question why we don't just "fix" the system-level stats. It may be useful to include the conclusions from that discussion, and why there is value in keeping the stats this way. > Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx> > Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
