Re: [RFC PATCH 10/15] virtio: virtio_balloon: use PAGES_PER_SECTION instead of MAX_ORDER_NR_PAGES.

[David Hildenbrand]

On 05.08.21 21:02, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> It keeps the existing behavior when MAX_ORDER grows beyond a section.

... but it breaks/changes existing behavior if MAX_ORDER is smaller than 
a section?

> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Jason Wang <jasowang@xxxxxxxxxx>
> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>   drivers/virtio/virtio_balloon.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 47dce91f788c..de8d0355d827 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -36,7 +36,7 @@
>   #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
>   					     __GFP_NOMEMALLOC)
>   /* The order of free page blocks to report to host */
> -#define VIRTIO_BALLOON_HINT_BLOCK_ORDER (MAX_ORDER - 1)
> +#define VIRTIO_BALLOON_HINT_BLOCK_ORDER (PFN_SECTION_SHIFT - 1)
>   /* The size of a free page block in bytes */
>   #define VIRTIO_BALLOON_HINT_BLOCK_BYTES \
>   	(1 << (VIRTIO_BALLOON_HINT_BLOCK_ORDER + PAGE_SHIFT))


--
Thanks,

David / dhildenb