[fedora-virt] disabling ksm by default

[Dan Kenigsberg]

On Fri, Oct 30, 2009 at 09:22:05PM +0200, Izik Eidus wrote:
> 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?

kernel is kept with ksm_run = KSM_RUN_MERGE by deafult (different from
upstream, God forbid!), but init.d/ksm runs by default and sets
max_kernel_pages to a reasonable value.

http://gitorious.org/ksm-control-scripts/ksm-control-scripts/commit/0a242288d0b7f3606e68ce2096e467e337d22c0a