On 10/20/2016 11:24 PM, 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
Why is it not efficient? How is using a bitmap more efficient? What
kinds of cases is the bitmap inefficient?
> 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.
Why did you choose to add these features to the structure? What
benefits do they add?
Could you describe your solution a bit here, and describe its strengths
and weaknesses?
The same comments apply, even if (especially if) you change the data
structure.
> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
> Cc: Amit Shah <amit.shah@xxxxxxxxxx>
> ---
> 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 {
> + /* Used to distinguish different request */
> + __virtio16 cmd;
> + /* Shift width of page in the bitmap */
> + __virtio16 page_shift;
> + /* flag used to identify different status */
> + __virtio16 flag;
> + /* Reserved */
> + __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 */
> + __virtio64 bmap_len;
> +};
FWIW this is totally unreadable. Please do something like this:
> +struct balloon_bmap_hdr {
> + __virtio16 cmd; /* Used to distinguish different ...
> + __virtio16 page_shift; /* Shift width of page in the bitmap */
> + __virtio16 flag; /* flag used to identify different...
> + __virtio16 reserved; /* Reserved */
> + __virtio64 req_id; /* ID of the request */
> + __virtio64 start_pfn; /* The pfn of 0 bit in the bitmap */
> + __virtio64 bmap_len; /* The length of the bitmap, in bytes */
> +};
and please make an effort to add useful comments. "/* Reserved */"
seems like a waste of bytes to me.
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