Messages in this thread | | | Date | Sun, 16 Aug 2009 11:28:22 +0800 | From | Wu Fengguang <> | Subject | Re: [RFC] respect the referenced bit of KVM guest pages? |
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On Thu, Aug 06, 2009 at 09:16:14PM +0800, Rik van Riel wrote: > Wu Fengguang wrote: > > > I guess both schemes have unacceptable flaws. > > > > For JVM/BIGMEM workload, most pages would be found referenced _all the time_. > > So the KEEP_MOST scheme could increase reclaim overheads by N=250 times; > > while the DROP_CONTINUOUS scheme is effectively zero cost. > > The higher overhead may not be an issue on smaller systems, > or inside smaller cgroups inside large systems, when doing > cgroup reclaim.
Right.
> > However, the DROP_CONTINUOUS scheme does bring more _indeterminacy_. > > It can behave vastly different on single active task and multi ones. > > It is short sighted and can be cheated by bursty activities. > > The split LRU VM tries to avoid the bursty page aging as > much as possible, by doing background deactivating of > anonymous pages whenever we reclaim page cache pages and > the number of anonymous pages in the zone (or cgroup) is > low.
Right, but I meant busty page allocations and accesses on them, which can make a large continuous segment of referenced pages in LRU list, say 50MB. They may or may not be valuable as a whole, however a local algorithm may keep the first 4MB and drop the remaining 46MB.
Thanks, Fengguang
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