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

[Li, Liang Z]

> Sent: Wednesday, January 18, 2017 3:11 AM
> To: Li, Liang Z
> Cc: kvm@xxxxxxxxxxxxxxx; virtio-dev@xxxxxxxxxxxxxxxxxxxx; qemu-
> devel@xxxxxxxxxx; linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; amit.shah@xxxxxxxxxx; Hansen,
> Dave; cornelia.huck@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> david@xxxxxxxxxx; aarcange@xxxxxxxxxx; dgilbert@xxxxxxxxxx;
> quintela@xxxxxxxxxx
> Subject: Re: [virtio-dev] Re: [PATCH v6 kernel 2/5] virtio-balloon: define new
> feature bit and head struct
> 
> On Fri, Jan 13, 2017 at 09:24:22AM +0000, Li, Liang Z wrote:
> > > 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@xxxxxxxxx>
> > > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > > Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
> > > > Cc: Amit Shah <amit.shah@xxxxxxxxxx>
> > > > Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> > > > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > > > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > > > ---
> > > >  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
> 
> Yes but first I would like to understand how come no fields in this new
> structure come up if I search for them in the following patch. I don't see why

It's not true, all of the field will be referenced in the following patches except 
the 'reserved' filed.

> should I waste time on reviewing the implementation if the interface isn't
> reasonable. You don't have to waste it too - just send RFC patches with the
> header until we can agree on it.

OK. I will post the header part separately.

Thanks!
Liang
> 
> --
> MST
> 
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