[fedora-virt] disabling ksm by default

Izik Eidus ieidus at redhat.com
Fri Oct 30 19:22:05 UTC 2009


On 10/27/2009 05:55 PM, Mark McLoughlin wrote:
> On Tue, 2009-10-27 at 10:46 -0500, Justin M. Forbes wrote:
>    
>> On Tue, 2009-10-27 at 17:31 +0200, Izik Eidus wrote:
>>      
>>> On 10/27/2009 04:42 PM, Justin M. Forbes wrote:
>>>
>>>        
>>>> While I do understand what you are saying, I don't think it is worth making
>>>> a kernel change for at this point in the cycle.  Because ksm itself has a
>>>> separate initscript, people who wish to use ksm will likely turn it on.
>>>> This sets the max_kernel_pages to a reasonable value.  People who are not
>>>> interested enough to turn on the ksm service are probably not the kind of
>>>> people who will be checking to see how effective ksm is at all.
>>>>
>>>>          
>>> To me it sound that users have no idea about this script, and ksm merge
>>> to him just the zero pages of windows 7...
>>>
>>> My feeling is that 99% of the ppl in the world that will use it, would
>>> just see the zero page merged and think "that is it..."
>>> The current behaivor in fedora 12 is misleading the user (at least it
>>> seems to me that it misslead that specific user)
>>>
>>> Btw we can set this value from userspace if we want "echo 0>
>>> /sys/kernel/mm/ksm/run"
>>>        
>> Where would we put that in userspace? Another init script? I just
>> updated to documentation on the feature page (and hopefully in the final
>> release notes) to say that ksm can be enabled by running 'sudo chkconfig
>> ksm on' in effort to draw more attention to these scripts.
>>
>> The other option is to make the ksm init script default to on, and just
>> leave ksmtuned off at system start.  Since ksm is on by the default
>> kernel, all we would be doing here is changing max_kernel_pages to a
>> machine specific value.  The ksm init script is part of the qemu
>> package, so it would only be changed on systems doing virt anyway.
>>      
> For Fedora 13, it'll be off by default in the kernel and the recommended
> way of switching it on is with 'chkconfig ksm on'
>
> For Fedora 12, it's on by default in the kernel, 'chkconfig ksm on' just
> changes max pages and the only way of disabling it is by manually
> writing zero to /sys/kernel/mm/ksm/run
>
> IMHO, if we are to change anything for Fedora 12, we should move closer
> to Fedora 13 behaviour, not further away from it - i.e. make it off by
> default in the kernel, but I'm fine with delaying that until post GA
>    

So what the result of this thread? you are delaying it to post GA?

> We'll probably end up with this behaviour in F12 updates at some point
> anyway when 2.6.32 is pulled in
>
> Cheers,
> Mark.
>
>    




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