Re: [Qemu-devel] [RESEND PATCH v3 kernel 2/7] virtio-balloon: define new feature bit and page bitmap head

[Michael S. Tsirkin]

On Fri, Oct 21, 2016 at 02:24:35PM +0800, Liang Li wrote:
> Add a new feature which supports sending the page information with
> a bitmap. The current implementation uses PFNs array, which is not
> very efficient. Using bitmap can improve the performance of
> inflating/deflating significantly
> 
> The page bitmap header will used to tell the host some information
> about the page bitmap. e.g. the page size, page bitmap length and
> start pfn.
> 
> Signed-off-by: Liang Li <address@hidden>
> Cc: Michael S. Tsirkin <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> Cc: Cornelia Huck <address@hidden>
> Cc: Amit Shah <address@hidden>
> ---
>  include/uapi/linux/virtio_balloon.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/include/uapi/linux/virtio_balloon.h 
> b/include/uapi/linux/virtio_balloon.h
> index 343d7dd..d3b182a 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -34,6 +34,7 @@
>  #define VIRTIO_BALLOON_F_MUST_TELL_HOST      0 /* Tell before reclaiming 
> pages */
>  #define VIRTIO_BALLOON_F_STATS_VQ    1 /* Memory Stats virtqueue */
>  #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM      2 /* Deflate balloon on OOM */
> +#define VIRTIO_BALLOON_F_PAGE_BITMAP 3 /* Send page info with bitmap */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12
> @@ -82,4 +83,22 @@ struct virtio_balloon_stat {
>       __virtio64 val;
>  } __attribute__((packed));
>  
> +/* Page bitmap header structure */
> +struct balloon_bmap_hdr {

Should be virtio_balloon.

> +     /* Used to distinguish different request */

different requests? what are the legal values?

> +     __virtio16 cmd;
> +     /* Shift width of page in the bitmap */

In which units?

> +     __virtio16 page_shift;
> +     /* flag used to identify different status */

this comment does not seem to add any value.

> +     __virtio16 flag;
> +     /* Reserved */

this too

> +     __virtio16 reserved;
> +     /* ID of the request */
> +     __virtio64 req_id;
> +     /* The pfn of 0 bit in the bitmap */
> +     __virtio64 start_pfn;
> +     /* The length of the bitmap, in bytes */

Why not in bits?

> +     __virtio64 bmap_len;
> +};
> +
>  #endif /* _LINUX_VIRTIO_BALLOON_H */
> -- 
> 1.8.3.1