linux-kernel - Re: [RFC 2/5] virtio_balloon: update the NR_BALLOON

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Message-ID: <20250312025331-mutt-send-email-mst@kernel.org>
Date: Wed, 12 Mar 2025 02:55:45 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Nico Pache <npache@...hat.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [RFC 2/5] virtio_balloon: update the NR_BALLOON_PAGES state

On Tue, Mar 11, 2025 at 06:06:57PM -0600, Nico Pache wrote:
> Update the NR_BALLOON_PAGES counter when pages are added to or
> removed from the virtio balloon.
> 
> Signed-off-by: Nico Pache <npache@...hat.com>
> ---
>  drivers/virtio/virtio_balloon.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 89da052f4f68..406414dbb477 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -274,6 +274,8 @@ static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num)
>  
>  		set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
>  		vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
> +		mod_node_page_state(page_pgdat(page), NR_BALLOON_PAGES,
> +			VIRTIO_BALLOON_PAGES_PER_PAGE);
>  		if (!virtio_has_feature(vb->vdev,
>  					VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
>  			adjust_managed_page_count(page, -1);


This means the counter is in virtio balloon page units, which
runs counter to the declared goal of making the interface
hypervisor-agnostic.


> @@ -324,6 +326,8 @@ static unsigned int leak_balloon(struct virtio_balloon *vb, size_t num)
>  		set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
>  		list_add(&page->lru, &pages);
>  		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> +		mod_node_page_state(page_pgdat(page), NR_BALLOON_PAGES,
> +			-VIRTIO_BALLOON_PAGES_PER_PAGE);


Same.

Thanks,

>  	}
>  
>  	num_freed_pages = vb->num_pfns;
> -- 
> 2.48.1