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Re: ksmd - what is expected behavior?



On Tue, Oct 27, 2009 at 11:48 AM, Justin M. Forbes <jmforbes linuxtx org> wrote:
> On Tue, Oct 27, 2009 at 09:20:20AM -0700, Tom London wrote:
>> On Tue, Oct 27, 2009 at 9:10 AM, Mark McLoughlin <markmc redhat com> wrote:
>> > On Tue, 2009-10-27 at 09:08 -0700, Tom London wrote:
>> > ...
>> >> But I notice that "ksm" appears off:
>> >>
>> >> [root tlondon init.d]# service ksm status
>> >> ksm is not running
>> >> [root tlondon init.d]# service ksmtuned status
>> >> ksmtuned (pid  2559) is running...
>> >> [root tlondon init.d]#
>> >>
>> >> Interesting tuning.... ;)
>> >>
>> >> Any idea what is going on?
>> >
>> > Yes, because ksmd (a kernel thread) is enabled by default, the ksm init
>> > script isn't needed to enable it currently
>> >
>> > However, in 2.6.32, ksmd is disabled by default and the ksm init script
>> > will be needed to enable it
>> >
>> > Cheers,
>> > Mark.
>> >
>> >
>> OK.  So is the "reasonable" setup to have "ksmtuned" enabled (to disable "ksm")?
>>
>> Or is it necessary to manually run "service ksmtuned start" manually.....
>>
> ksmtuned is not really there to disable ksm, it will enable and disable
> based on what the system is doing... It checks every so often and resets
> ksm if it sees a need.  Ideally you would have both ksm and ksmtuned on.
> The ksm service will enable ksm if it is disabled, but more importantly it
> sets the number of pages ksm can use to half of memory instead of the
> horribly low 2k default.  The ksm service would start, set the limits and
> turn on ksm if it were off.  The ksmtuned would then start and check the
> system, make sure ksm has done the work it needs to based on what the
> system is running and then turn off ksm.  Chances are when ksmtuned makes
> its first pass, there is no mergeable memory so it just shuts off ksm. Once
> you start a few vms, ksmtuned will notice this on the next wakeup and
> enable ksm long enough to scan and do its job.
>
> Justin
>
Thanks.

I'll set both ksm and ksmtuned to "enabled" and see what happens on
the next boot.

tom
-- 
Tom London


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