Re: [PATCH v6 26/29] KVM: Optimize gfn lookup in kvm_zap_gfn_range()

[Maciej S. Szmigiero]

On 01.12.2021 04:41, Sean Christopherson wrote:
> On Tue, Nov 30, 2021, Maciej S. Szmigiero wrote:
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 41efe53cf150..6fce6eb797a7 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -848,6 +848,105 @@ struct kvm_memory_slot *id_to_memslot(struct kvm_memslots *slots, int id)
> >   	return NULL;
> >   }
> >   
> > +/* Iterator used for walking memslots that overlap a gfn range. */
> > +struct kvm_memslot_iter {
> > +	struct kvm_memslots *slots;
> > +	gfn_t end;
> > +	struct rb_node *node;
> > +};
>
> ...
>
> > +static inline struct kvm_memory_slot *kvm_memslot_iter_slot(struct kvm_memslot_iter *iter)
> > +{
> > +	return container_of(iter->node, struct kvm_memory_slot, gfn_node[iter->slots->node_idx]);
>
> Having to use a helper in callers of kvm_for_each_memslot_in_gfn_range() is a bit
> ugly, any reason not to grab @slot as well?  Then the callers just do iter.slot,
> which IMO is much more readable.

"slot" can be easily calculated from "node" together with either "slots" or
"node_idx" (the code above just adjusts a pointer) so storing it in the
iterator makes little sense if the later are already stored there.

> And if we do that, I'd also vote to omit slots and end from the iterator.  It would
> mean passing in slots and end to kvm_memslot_iter_is_valid() and kvm_memslot_iter_next(),
> but that's more idiomatic in a for-loop if iter is considered to be _just_ the iterator
> part.  "slots" is arguable, but "end" really shouldn't be part of the iterator.

You're right that we can get away with not storing "end", will remove it.

Thanks,
Maciej