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

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Message-ID: <328b00e2-d2ac-7efb-a3d9-a6e9933d85a8@redhat.com>
Date:   Tue, 19 Nov 2019 12:38:05 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Wei Wang <wei.w.wang@...el.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 2/2] virtio_balloon: divide/multiply instead of shifts

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@...hat.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@...hat.com>

-- 

Thanks,

David / dhildenb