Re: [PATCH] KVM: s390: remove delayed reallocation of page tables for KVM

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/04/2015 13:43, Christian Borntraeger wrote:
>> > 
>> > Couldn't you make this a hidden kconfig option that gets automatically selected when kvm is enabled? Or is there a non-kvm case that needs it too?
> For things like RHEV the default could certainly be "enabled", but for normal
> distros like SLES/RHEL, the idea was to NOT enable that by default, as the non-KVM
> case is more common and might suffer from the additional memory consumption of
> the page tables. (big databases come to mind)
> 
> We could think about having rpms like kvm to provide a sysctl file that sets it if we
> want to minimize the impact. Other ideas?

I can say what _won't_ work which is tying it to the KVM module.
Nowadays it is loaded automatically via udev on the first /dev/kvm
access, and that's already too late because qemu-kvm's page tables have
been created already.  Right?

With my Fedora hat on, adding a sysctl file to the userspace RPMs (e.g.
qemu) would work.  CCing Cole Robinson who is the main maintainer of the
Fedora virt packages.

Paolo