Re: [PATCH v4 1/2] KVM: s390: add stat counter for shadow gmap events

[Janosch Frank <frankja@linux.ibm.com>]

On 10/9/23 11:32, Nico Boehr wrote:
> The shadow gmap tracks memory of nested guests (guest-3). In certain
> scenarios, the shadow gmap needs to be rebuilt, which is a costly operation
> since it involves a SIE exit into guest-1 for every entry in the respective
> shadow level.
> 
> Add kvm stat counters when new shadow structures are created at various
> levels. Also add a counter gmap_shadow_create when a completely fresh
> shadow gmap is created as well as a counter gmap_shadow_reuse when an
> existing gmap is being reused.
> 
> Note that when several levels are shadowed at once, counters on all
> affected levels will be increased.
> 
> Also note that not all page table levels need to be present and a ASCE
> can directly point to e.g. a segment table. In this case, a new segment
> table will always be equivalent to a new shadow gmap and hence will be
> counted as gmap_shadow_create and not as gmap_shadow_segment.
> 
> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>