On Fri, May 8, 2020 at 9:38 PM Johannes Weiner <han...@cmpxchg.org> wrote: > > On Fri, May 08, 2020 at 06:25:14AM -0700, Shakeel Butt wrote: > > On Fri, May 8, 2020 at 3:34 AM Yafang Shao <laoar.s...@gmail.com> wrote: > > > > > > On Fri, May 8, 2020 at 4:49 AM Shakeel Butt <shake...@google.com> 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. > > > > > > > > > > Hi Shakeel, > > > > > > We always use pgscan and pgsteal for monitoring the system level > > > memory pressure, for example, by using sysstat(sar) or some other > > > monitor tools. > > I'm in the same boat. It's useful to have activity that happens purely > due to machine capacity rather than localized activity that happens > due to the limits throughout the cgroup tree. >
Hi Johannes, When I used PSI to monitor memory pressure, I found there's the same behavoir in PSI that /proc/pressure/{memroy, IO} can be very large due to some limited cgroups rather the machine capacity. Should we separate /proc/pressure/XXX from /sys/fs/cgroup/XXX.pressure as well ? Then /proc/pressure/XXX only indicate the pressure due to machine capacity and /sys/fs/cgroup/XXX.presssure show the pressure throughout the cgroup tree. Besides that, there's another difference between /proc/pressure/XXX and /sys/fs/cgroup/XXX.pressure, which is when you disable the psi (i.e. psi=n) /proc/pressure/ will disapear but /sys/fs/cgroup/XXX.pressure still exist. If we separate them, this difference will be reasonable. > > Don't you need pgrefill in addition to pgscan and pgsteal to get the > > full picture of the reclaim activity? > > I actually almost never look at pgrefill. > > > > But with this change, these two counters include the memcg pressure as > > > well. It is not easy to know whether the pgscan and pgsteal are caused > > > by system level pressure or only some specific memcgs reaching their > > > memory limit. > > > > > > How about adding cgroup_reclaim() to pgrefill as well ? > > > > > > > I am looking for all the reclaim activity on the system. Adding > > !cgroup_reclaim to pgrefill will skip the cgroup reclaim activity. > > Maybe adding pgsteal_cgroup and pgscan_cgroup would be better. > > How would you feel about adding memory.stat at the root cgroup level? > > 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. -- Thanks Yafang