SuperPages utilization survey
Ulrich Spörlein
uqs at FreeBSD.org
Fri Jun 1 19:04:04 UTC 2012
On Fri, 2012-06-01 at 14:23:42 +0200, Ivan Voras wrote:
> hello,
>
> I was wondering how much usage superpages get in real-world systems, and
> made a small script to parse the output of "procstat -va":
>
> http://people.freebsd.org/~ivoras/stuff/spsurvey.py
>
> The results from three systems (with the script being run as root) are here:
>
> http://people.freebsd.org/~ivoras/stuff/spsurvey_desktop.txt
> http://people.freebsd.org/~ivoras/stuff/spsurvey_mixserver.txt
> http://people.freebsd.org/~ivoras/stuff/spsurvey_webserver.txt
>
> What I get from it is that they are really under-utilized, probably
> because it's a rare occasion that every single page in a 2 MB region is
> touched to enable its promotion.
>
> The only good case seems to be the third one, with the database
> accessing the whole memory range a lot, but the statistics which
> procstat reports is inaccurate: there could be only a single superpage
> in the whole region and procstat will make the region with the "S" flag.
>
> If there's anyone else wishing to run the script and post the results,
> it could be useful to see.
Here's output of a machine doing basically nothing all day:
% fetch -o- http://people.freebsd.org/\~ivoras/stuff/spsurvey.py | sudo python -
- 100% of 2035 B 664 kBps
last pid: 20460; load averages: 0.04, 0.01, 0.00 up 2+01:35:37 21:01:08
49 processes: 1 running, 48 sleeping
Mem: 104M Active, 2079M Inact, 1593M Wired, 34M Cache, 418M Buf, 133M Free
Swap: 4096M Total, 1376K Used, 4095M Free
Total accounted memory mappings: 1669 MB (427314 pages)
Memory in superpages: 12 MB (2 mappings)
+ pid: 864 (named) start: 802800000 stop: 803000000 (8 MB) tp: df path:
+ pid: 1002 (slapd) start: 805400000 stop: 805800000 (4 MB) tp: df path:
Eligible mappings not promoted: 66
...
Also, what about kernel mappings? With ZFS and stuff there should be
more superpages in kernel memory, no?
Uli
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