On Thu, Jul 26, 2018 at 11:07:32AM +1000, Singh, Balbir wrote: > On 7/25/18 1:15 AM, Johannes Weiner wrote: > > On Tue, Jul 24, 2018 at 07:14:02AM +1000, Balbir Singh wrote: > >> Does the mechanism scale? I am a little concerned about how frequently > >> this infrastructure is monitored/read/acted upon. > > > > I expect most users to poll in the frequency ballpark of the running > > averages (10s, 1m, 5m). Our OOMD defaults to 5s polling of the 10s > > average; we collect the 1m average once per minute from our machines > > and cgroups to log the system/workload health trends in our fleet. > > > > Suren has been experimenting with adaptive polling down to the > > millisecond range on Android. > > > > I think this is a bad way of doing things, polling only adds to > overheads, there needs to be an event driven mechanism and the > selection of the events need to happen in user space. Of course, I'm not saying you should be doing this, and in fact Suren and I were talking about notification/event infrastructure. You asked if this scales and I'm telling you it's not impossible to read at such frequencies. Maybe you can clarify your question. > >> Why aren't existing mechanisms sufficient > > > > Our existing stuff gives a lot of indication when something *may* be > > an issue, like the rate of page reclaim, the number of refaults, the > > average number of active processes, one task waiting on a resource. > > > > But the real difference between an issue and a non-issue is how much > > it affects your overall goal of making forward progress or reacting to > > a request in time. And that's the only thing users really care > > about. It doesn't matter whether my system is doing 2314 or 6723 page > > refaults per minute, or scanned 8495 pages recently. I need to know > > whether I'm losing 1% or 20% of my time on overcommitted memory. > > > > Delayacct is time-based, so it's a step in the right direction, but it > > doesn't aggregate tasks and CPUs into compound productivity states to > > tell you if only parts of your workload are seeing delays (which is > > often tolerable for the purpose of ensuring maximum HW utilization) or > > your system overall is not making forward progress. That aggregation > > isn't something you can do in userspace with polled delayacct data. > > By aggregation you mean cgroup aggregation? System-wide and per cgroup.
