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Re: [fedora-virt] disabling ksm by default



On Fri, Oct 30, 2009 at 10:04:20AM -0500, Justin M. Forbes wrote:
> On Fri, Oct 30, 2009 at 10:00:28AM +0000, Richard W.M. Jones wrote:
> > On Tue, Oct 27, 2009 at 10:12:49AM +0000, Mark McLoughlin wrote:
> > > ksm is disabled by default currently
> > [...]
> > >   # unless KSM_MAX_KERNEL_PAGES is set, let ksm munch up to half of total memory.
> > 
> > Mark, can you summarise why we wouldn't want KSM to be enabled by
> > default, and why we need to limit it to half of total memory?
> > 
> The limit to half of total memory is because ksm pages are unswappable at
> this time.  To be fixed in a future kernel.  As for  enabling by default,
> the more I think about it, the more this makes sense.  The ksm initscript
> is shipped with qemu, so anyone with it installed should be interested in
> virt, and the value of max_kernel_pages doesn't matter if you are not
> running anything which marks memory mergeable, which only kvm does at the
> moment.

Having `chkconfig ksm on` by default is great.
I just want to see that the kernel thread, which ksm service controls,
is not running until the service has started. As you say, when there are
no qemu processes, the kernel thread has very low cost. But it also has
zero value. So why have it running?


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