Re: [PATCH v2] KVM: PPC: Book3S HV: Make the guest hash table size configurable

[Alexander Graf <agraf@suse.de>]

On 05/04/2012 02:32 PM, Paul Mackerras wrote:
> This adds a new ioctl to enable userspace to control the size of the guest
> hashed page table (HPT) and to clear it out when resetting the guest.
> The KVM_PPC_ALLOCATE_HTAB ioctl is a VM ioctl and takes as its parameter
> a pointer to a u32 containing the desired order of the HPT (log base 2
> of the size in bytes), which is updated on successful return to the
> actual order of the HPT which was allocated.
>
> There must be no vcpus running at the time of this ioctl.  To enforce
> this, we now keep a count of the number of vcpus running in
> kvm->arch.vcpus_running.
>
> If the ioctl is called when a HPT has already been allocated, we don't
> reallocate the HPT but just clear it out.  We first clear the
> kvm->arch.rma_setup_done flag, which has two effects: (a) since we hold
> the kvm->lock mutex, it will prevent any vcpus from starting to run until
> we're done, and (b) it means that the first vcpu to run after we're done
> will re-establish the VRMA if necessary.
>
> If userspace doesn't call this ioctl before running the first vcpu, the
> kernel will allocate a default-sized HPT at that point.  We do it then
> rather than when creating the VM, as the code did previously, so that
> userspace has a chance to do the ioctl if it wants.
>
> When allocating the HPT, we can allocate either from the kernel page
> allocator, or from the preallocated pool.  If userspace is asking for
> a different size from the preallocated HPTs, we first try to allocate
> using the kernel page allocator.  Then we try to allocate from the
> preallocated pool, and then if that fails, we try allocating decreasing
> sizes from the kernel page allocator, down to the minimum size allowed
> (256kB).  Note that the kernel page allocator limits allocations to
> 1<<  CONFIG_FORCE_MAX_ZONEORDER pages, which by default corresponds to
> 16MB (on 64-bit powerpc, at least).
>
> Signed-off-by: Paul Mackerras<paulus@samba.org>

Thanks, applied to kvm-ppc-next.


Alex