linux-kernel - Re: [PATCH v2 7/7] virtio_balloon: Stop calling page_address() in free

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Message-ID: <5ee2b684-94d9-40be-b01c-b0538ced33bc@redhat.com>
Date: Wed, 27 Aug 2025 14:01:01 +0200
From: David Hildenbrand <david@...hat.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v2 7/7] virtio_balloon: Stop calling page_address() in
 free_pages()

On 26.08.25 22:56, Vishal Moola (Oracle) wrote:
> free_pages() should be used when we only have a virtual address. We
> should call __free_pages() directly on our page instead.
> 
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> ---
>   drivers/virtio/virtio_balloon.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index eae65136cdfb..d4e6865ce355 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -488,8 +488,7 @@ static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
>   		page = balloon_page_pop(&vb->free_page_list);
>   		if (!page)
>   			break;
> -		free_pages((unsigned long)page_address(page),
> -			   VIRTIO_BALLOON_HINT_BLOCK_ORDER);
> +		__free_pages(page, VIRTIO_BALLOON_HINT_BLOCK_ORDER);
>   	}
>   	vb->num_free_page_blocks -= num_returned;
>   	spin_unlock_irq(&vb->free_page_list_lock);

I think you missed another nastiness of similar kind in 
get_free_page_and_send() where we do

	p = page_address(page);

Just to call

	free_pages((unsigned long)p, VIRTIO_BALLOON_HINT_BLOCK_ORDER);

-- 
Cheers

David / dhildenb