Re: [PATCH 2/2] virtio_balloon: divide/multiply instead of shifts

David Hildenbrand
2019-11-19T11:38:17Z

On 19.11.19 11:29, Michael S. Tsirkin wrote:
> We managed to get confused about the shift direction at least once.
> Let's switch to division/multiplcation instead. Add a number of pages
> macro for this purpose. We still keep the order macro around too since
> this is what alloc/free pages want.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/virtio/virtio_balloon.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index b6a95cd28d9f..dc1ebd638e9b 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -36,6 +36,7 @@
> /* The size of a free page block in bytes */
> #define VIRTIO_BALLOON_HINT_BLOCK_BYTES \
> (1 << (VIRTIO_BALLOON_HINT_BLOCK_ORDER + PAGE_SHIFT))
> +#define VIRTIO_BALLOON_HINT_BLOCK_PAGES (1 << VIRTIO_BALLOON_HINT_BLOCK_ORDER)
>
> #ifdef CONFIG_BALLOON_COMPACTION
> static struct vfsmount *balloon_mnt;
> @@ -765,11 +766,11 @@ static unsigned long shrink_free_pages(struct virtio_balloon *vb,
> unsigned long blocks_to_free, blocks_freed;
>
> pages_to_free = round_up(pages_to_free,
> - 1 << VIRTIO_BALLOON_HINT_BLOCK_ORDER);
> - blocks_to_free = pages_to_free >> VIRTIO_BALLOON_HINT_BLOCK_ORDER;
> + VIRTIO_BALLOON_HINT_BLOCK_PAGES);
> + blocks_to_free = pages_to_free / VIRTIO_BALLOON_HINT_BLOCK_PAGES;
> blocks_freed = return_free_pages_to_mm(vb, blocks_to_free);
>
> - return blocks_freed << VIRTIO_BALLOON_HINT_BLOCK_ORDER;
> + return blocks_freed * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
> }
>
> static unsigned long leak_balloon_pages(struct virtio_balloon *vb,
> @@ -825,7 +826,7 @@ static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
> unsigned long count;
>
> count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
> - count += vb->num_free_page_blocks << VIRTIO_BALLOON_HINT_BLOCK_ORDER;
> + count += vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
>
> return count;
> }
>

Reviewed-by: David Hildenbrand <david@redhat.com>

--

Thanks,

David / dhildenb