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Subject: Re: [PATCH 2/2] virtio_balloon: divide/multiply instead of shifts
To:     "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org
Cc:     Wei Wang <wei.w.wang@intel.com>,
        Khazhismel Kumykov <khazhy@google.com>,
        Jason Wang <jasowang@redhat.com>,
        virtualization@lists.linux-foundation.org
References: <20191119102838.39380-1-mst@redhat.com>
 <20191119102838.39380-2-mst@redhat.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <328b00e2-d2ac-7efb-a3d9-a6e9933d85a8@redhat.com>
Date:   Tue, 19 Nov 2019 12:38:05 +0100
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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.
>=20
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>   drivers/virtio/virtio_balloon.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
>=20
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_ball=
oon.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 \
>   =09(1 << (VIRTIO_BALLOON_HINT_BLOCK_ORDER + PAGE_SHIFT))
> +#define VIRTIO_BALLOON_HINT_BLOCK_PAGES (1 << VIRTIO_BALLOON_HINT_BLOCK_=
ORDER)
>  =20
>   #ifdef CONFIG_BALLOON_COMPACTION
>   static struct vfsmount *balloon_mnt;
> @@ -765,11 +766,11 @@ static unsigned long shrink_free_pages(struct virti=
o_balloon *vb,
>   =09unsigned long blocks_to_free, blocks_freed;
>  =20
>   =09pages_to_free =3D round_up(pages_to_free,
> -=09=09=09=09 1 << VIRTIO_BALLOON_HINT_BLOCK_ORDER);
> -=09blocks_to_free =3D pages_to_free >> VIRTIO_BALLOON_HINT_BLOCK_ORDER;
> +=09=09=09=09 VIRTIO_BALLOON_HINT_BLOCK_PAGES);
> +=09blocks_to_free =3D pages_to_free / VIRTIO_BALLOON_HINT_BLOCK_PAGES;
>   =09blocks_freed =3D return_free_pages_to_mm(vb, blocks_to_free);
>  =20
> -=09return blocks_freed << VIRTIO_BALLOON_HINT_BLOCK_ORDER;
> +=09return blocks_freed * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
>   }
>  =20
>   static unsigned long leak_balloon_pages(struct virtio_balloon *vb,
> @@ -825,7 +826,7 @@ static unsigned long virtio_balloon_shrinker_count(st=
ruct shrinker *shrinker,
>   =09unsigned long count;
>  =20
>   =09count =3D vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
> -=09count +=3D vb->num_free_page_blocks << VIRTIO_BALLOON_HINT_BLOCK_ORDE=
R;
> +=09count +=3D vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES=
;
>  =20
>   =09return count;
>   }
>=20

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

--=20

Thanks,

David / dhildenb