[fedora-virt] does ksm really work?

[Dor Laor]

On 09/19/2010 10:17 AM, Dan Kenigsberg wrote:
> On Sat, Sep 18, 2010 at 10:58:39PM -0400, sean darcy wrote:
>> I'm running kvm on F14. I'm running 2 XP clones. The ksm and ksmtuned
>> demons are running.
>>
>> Yet:
>>
>>   for ii in /sys/kernel/mm/ksm/* ; do echo -n "$ii: " ; cat $ii ; done
>> /sys/kernel/mm/ksm/full_scans: 0
>> /sys/kernel/mm/ksm/pages_shared: 0
>> /sys/kernel/mm/ksm/pages_sharing: 0
>> /sys/kernel/mm/ksm/pages_to_scan: 100
>> /sys/kernel/mm/ksm/pages_unshared: 0
>> /sys/kernel/mm/ksm/pages_volatile: 266200
>> /sys/kernel/mm/ksm/run: 0
>> /sys/kernel/mm/ksm/sleep_millisecs: 20
>>
>> And yes, I've echo'd 1 to sys/kernel/mm/ksm/run, but it gets reset to
>> 0 after about a minute (ksmtuned at work?).
>>
>> When does ksm do its stuff? This is a pretty big machine (16G). Does
>> it wait until there's memory pressure?
>
> Yes, ksmtuned does exactly that. If you prefer to control ksm/run
> yourself, you can shut this service down.

If you have sufficient memory on the host, ksm won't scan until the free 
ram pages will cross some water mark.
Check /etc/ksmtuned.conf and watch the log file if debug is enabled.

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