Re: [RFC 4/5] vmx_balloon: update the NR_BALLOON_PAGES state

[David Hildenbrand <david@xxxxxxxxxx>]

On 12.03.25 21:11, Nico Pache wrote:
> On Wed, Mar 12, 2025 at 12:57 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> > On Tue, Mar 11, 2025 at 06:06:59PM -0600, Nico Pache wrote:
> > > Update the NR_BALLOON_PAGES counter when pages are added to or
> > > removed from the VMware balloon.
> > >
> > > Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
> > > ---
> > >   drivers/misc/vmw_balloon.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
> > > index c817d8c21641..2c70b08c6fb3 100644
> > > --- a/drivers/misc/vmw_balloon.c
> > > +++ b/drivers/misc/vmw_balloon.c
> > > @@ -673,6 +673,8 @@ static int vmballoon_alloc_page_list(struct vmballoon *b,
> > >
> > >                        vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_ALLOC,
> > >                                                 ctl->page_size);
> > > +                     mod_node_page_state(page_pgdat(page), NR_BALLOON_PAGES,
> > > +                             vmballoon_page_in_frames(ctl->page_size));
> >
> > same issue as virtio I think - this counts frames not pages.
> I agree with the viritio issue since PAGE_SIZE can be larger than
> VIRTIO_BALLOON_PFN_SHIFT, resulting in multiple virtio_balloon pages
> for each page. I fixed that one, thanks!
>
> For the Vmware one, the code is littered with mentions of counting in
> 4k or 2M but as far as I can tell from looking at the code it actually
> operates in PAGE_SIZE or PMD size chunks and this count would be
> correct.
> Perhaps I am missing something though.
vmballoon_page_in_frames() documents to "Return: the number of 4k 
frames.", because it supports either 4k or 2M chunks IIRC.
I think the catch is that PAGE_SIZE will in these configs always be 4k. 
Otherwise things like vmballoon_mark_page_offline() wouldn't work as 
expected.
So I think this is correct.

--
Cheers,

David / dhildenb