[fedora-virt] disabling ksm by default

Izik Eidus ieidus at redhat.com
Tue Oct 27 10:24:13 UTC 2009


On 10/27/2009 12:12 PM, Mark McLoughlin wrote:
> Hi Izik,
>
> On Tue, 2009-10-27 at 00:55 +0200, Izik Eidus wrote:
>    
>> Hi, I saw that Fedora 12 will have ksm tunning script that control the
>> ksm speed / kernel pages allocation.
>>
>> The only problem that I have is - as far as I remember ksm is by default
>> enabled and only with 2000 kernel pages...
>> What I am worried about is that users wont use the ksm tunning script
>> and would just run ksm with this 2000 kernel pages -
>> the result would be that ksm will probably merge just the zero pages
>> (that could be alot of memory) and the user might not know
>> that much more memory can be saved...
>>
>> Is it possible to at least make ksm disabled by default? so the users
>> will have to run the ksm tunning script when they want to start ksm?
>>      
> ksm is disabled by default currently
>    

Ok so we are fine then.

>    
>> And if we set it to disabled by default, cant we set the initialized
>> values into more realistic value? (like 1/4 of the memory in the
>> mainline kernels? )
>>      
> Here's the logic we have in the init script:
>
>    # unless KSM_MAX_KERNEL_PAGES is set, let ksm munch up to half of total memory.
>    default_max_kernel_pages () {
>        local total pagesize
>        total=`awk '/^MemTotal:/ {print $2}' /proc/meminfo`
>        pagesize=`getconf PAGESIZE`
>        echo $[total * 1024 / pagesize / 2]
>    }
>
> git tree for the scripts here:
>
>    http://gitorious.org/ksm-control-scripts/ksm-control-scripts
>
> Suggestions, comments, patches etc. welcome
>
>    

Thanks.




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