Messages in this thread | | | Date | Tue, 23 Mar 2010 15:07:39 +0200 | From | Avi Kivity <> | Subject | Re: KSM & hugepages |
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On 03/23/2010 01:32 PM, Michael Tokarev wrote: > Hello. > > I noticed an interesting thing here, with qemu-kvm, KSM and > hugepages. > > When I initially enabled KSM, for my two windows guests I've > seen ~100 000 pages in /sys/kernel/mm/ksm/pages_shared . > That's quite good, and overall memory usage improved. > > Now, I also enabled hugepages in kvm, which speed things > up quite significantly (the speedup is noticeable). > > But now, when both KSM and hugepages are activated, I don't > see KSM in action anymore. /sys/../mm/pages_shared shows > 56 pages, which is nothing. > > So I wonder what's up: > o that's 56 _huge_ pages (which means the actual saving > is 56*2M = 112Mb, which isn't really bad). If that's > the case, /sys/../mm/ interface lacks proper units > reporting; > o due to large pages there's much less chance to find > two pages with identical contents, so very little can > be shared; > o KSM does not scan hugepages at all > o something else. > > What is the issue here? > >
Those pages aren't scanned since ksm only scans anonymous memory; hugetlbfs is file backed memory. Even if it were anonymous memory, ksm doesn't support merging large pages (and the probability of finding a match is practically nil). No idea where the 56 comes from - perhaps a leak from the previous runs?
-- error compiling committee.c: too many arguments to function
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