linux-kernel - Re: [RFC 4/5] vmx_balloon: update the NR_BALLOON

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Message-ID: <CAA1CXcDjEErb2L85gi+W=1sFn73VHLto09nG6f1vS+10o4PctA@mail.gmail.com>
Date: Wed, 12 Mar 2025 14:11:09 -0600
From: Nico Pache <npache@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, 
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Subject: Re: [RFC 4/5] vmx_balloon: update the NR_BALLOON_PAGES state

On Wed, Mar 12, 2025 at 12:57 AM Michael S. Tsirkin <mst@...hat.com> 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@...hat.com>
> > ---
> >  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.

>
> >               }
> >
> >               if (page) {
> > @@ -915,6 +917,8 @@ static void vmballoon_release_page_list(struct list_head *page_list,
> >       list_for_each_entry_safe(page, tmp, page_list, lru) {
> >               list_del(&page->lru);
> >               __free_pages(page, vmballoon_page_order(page_size));
> > +             mod_node_page_state(page_pgdat(page), NR_BALLOON_PAGES,
> > +                     -vmballoon_page_in_frames(page_size));
> >       }
> >
> >       if (n_pages)
> > @@ -1129,7 +1133,6 @@ static void vmballoon_inflate(struct vmballoon *b)
> >
> >               /* Update the balloon size */
> >               atomic64_add(ctl.n_pages * page_in_frames, &b->size);
> > -
>
>
> unrelated change
Fixed, Thanks for reviewing!
>
> >               vmballoon_enqueue_page_list(b, &ctl.pages, &ctl.n_pages,
> >                                           ctl.page_size);
> >
> > --
> > 2.48.1
>