Re: [RFC 1/5] meminfo: add a per node counter for balloon drivers

[Nico Pache <npache@redhat.com>]

On Thu, Mar 13, 2025 at 2:22 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 13.03.25 00:04, Nico Pache wrote:
> > On Wed, Mar 12, 2025 at 4:19 PM David Hildenbrand <david@redhat.com> wrote:
> >>
> >> On 12.03.25 01:06, Nico Pache wrote:
> >>> Add NR_BALLOON_PAGES counter to track memory used by balloon drivers and
> >>> expose it through /proc/meminfo and other memory reporting interfaces.
> >>
> >> In balloon_page_enqueue_one(), we perform a
> >>
> >> __count_vm_event(BALLOON_INFLATE)
> >>
> >> and in balloon_page_list_dequeue
> >>
> >> __count_vm_event(BALLOON_DEFLATE);
> >>
> >>
> >> Should we maybe simply do the per-node accounting similarly there?
> >
> > I think the issue is that some balloon drivers use the
> > balloon_compaction interface while others use their own.
> >
> > This would require unifying all the drivers under a single api which
> > may be tricky if they all have different behavior
>
> Why would that be required? Simply implement it in the balloon
> compaction logic, and in addition separately in the ones that don't
> implement it.

Ah ok that makes sense!

>
> That's the same as how we handle PageOffline today.
>
> In summary, we have
>
> virtio-balloon: balloon compaction
> hv-balloon: no balloon compaction
> xen-balloon: no balloon compaction
> vmx-balloon: balloon compaction
> pseries-cmm: balloon compaction

I'm having a hard time verifying this... it looks like only
vmx-balloon uses the balloon_compaction balloon_page_list_enqueue
function that calls balloon_page_enqueue_one.

>
> So you'd handle 3 balloon drivers in one go.
>
> (this series didn't touch pseries-cmm)
Ah I didn't realize that was a balloon driver. Ill add that one to the todo.
>
> --
> Cheers,
>
> David / dhildenb
>