RE: [virtio-dev] Re: [PATCH v6 kernel 2/5] virtio-balloon: define new feature bit and head struct

["Li, Liang Z" <liang.z.li@intel.com>]

> On Wed, Dec 21, 2016 at 02:52:25PM +0800, Liang Li wrote:
> > Add a new feature which supports sending the page information with
> > range array. The current implementation uses PFNs array, which is not
> > very efficient. Using ranges can improve the performance of
> > inflating/deflating significantly.
> >
> > Signed-off-by: Liang Li <liang.z.li@intel.com>
> > Cc: Michael S. Tsirkin <mst@redhat.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > Cc: Amit Shah <amit.shah@redhat.com>
> > Cc: Dave Hansen <dave.hansen@intel.com>
> > Cc: Andrea Arcangeli <aarcange@redhat.com>
> > Cc: David Hildenbrand <david@redhat.com>
> > ---
> >  include/uapi/linux/virtio_balloon.h | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/include/uapi/linux/virtio_balloon.h
> > b/include/uapi/linux/virtio_balloon.h
> > index 343d7dd..2f850bf 100644
> > --- a/include/uapi/linux/virtio_balloon.h
> > +++ b/include/uapi/linux/virtio_balloon.h
> > @@ -34,10 +34,14 @@
> >  #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_RANGE	3 /* Send page info
> with ranges */
> >
> >  /* Size of a PFN in the balloon interface. */  #define
> > VIRTIO_BALLOON_PFN_SHIFT 12
> >
> > +/* Bits width for the length of the pfn range */
> 
> What does this mean? Couldn't figure it out.
> 
> > +#define VIRTIO_BALLOON_NR_PFN_BITS 12
> > +
> >  struct virtio_balloon_config {
> >  	/* Number of pages host wants Guest to give up. */
> >  	__u32 num_pages;
> > @@ -82,4 +86,12 @@ struct virtio_balloon_stat {
> >  	__virtio64 val;
> >  } __attribute__((packed));
> >
> > +/* Response header structure */
> > +struct virtio_balloon_resp_hdr {
> > +	__le64 cmd : 8; /* Distinguish different requests type */
> > +	__le64 flag: 8; /* Mark status for a specific request type */
> > +	__le64 id : 16; /* Distinguish requests of a specific type */
> > +	__le64 data_len: 32; /* Length of the following data, in bytes */
> 
> This use of __le64 makes no sense.  Just use u8/le16/le32 pls.
> 

Got it, will change in the next version. 

And could help take a look at other parts? as well as the QEMU part.

Thanks!
Liang