On Fri, Jan 22, 2016 at 12:11:21PM -0500, Johannes Weiner wrote: > Hi, > > On Fri, Jan 22, 2016 at 10:56:15AM -0500, Rik van Riel wrote: > > I am trying to gauge interest in discussing VM containers at the LSF/MM > > summit this year. Projects like ClearLinux, Qubes, and others are all > > trying to use virtual machines as better isolated containers. > > > > That changes some of the goals the memory management subsystem has, > > from "use all the resources effectively" to "use as few resources as > > necessary, in case the host needs the memory for something else". > > I would be very interested in discussing this topic, because I think > the issue is more generic than these VM applications. We are facing > the same issues with regular containers, where aggressive caching is > counteracting the desire to cut down workloads to their bare minimum > in order to pack them as tightly as possible. > > With per-cgroup LRUs and thrash detection, we have infrastructure in By thrash detection, do you mean vmpressure? > place that could allow us to accomplish this. Right now we only enter > reclaim once memory runs out, but we could add an allocation mode that > would prefer to always reclaim from the local LRU before increasing > the memory footprint, and only expand once we detect thrashing in the > page cache. That would keep the workloads neatly trimmed at all times. I don't get it. Do you mean a sort of special GFP flag that would force the caller to reclaim before actual charging/allocation? Or is it supposed to be automatic, basing on how memcg is behaving? If the latter, I suppose it could be already done by a userspace daemon by adjusting memory.high as needed, although it's unclear how to do it optimally. > > For virtualized environments, the thrashing information would be > communicated slightly differently to the page allocator and/or the > host, but otherwise the fundamental principles should be the same. > > We'd have to figure out how to balance the aggressiveness there and > how to describe this to the user, as I can imagine that users would > want to tune this based on a tolerance for the degree of thrashing: if > pages are used every M ms, keep them cached; if pages are used every N > ms, freeing up the memory and refetching them from disk is better etc. Sounds reasonable. What about adding a parameter to memcg that would define ws access time? So that it would act just like memory.low, but in terms of lruvec age instead of lruvec size. I mean, we keep track of lruvec ages and scan those lruvecs whose age is > ws access time before others. That would protect those workloads that access their ws quite, but not very often from streaming workloads which can generate a lot of useless pressure. Thanks, Vladimir > > And we don't have thrash detection in secondary slab caches (yet). > > > Are people interested in discussing this at LSF/MM, or is it better > > saved for a different forum? > > If more people are interested, I think that could be a great topic. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
