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

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> 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?
> 

Will elaborate the solution in V4.

> >  /* 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.

OK. Maybe 'padding' is better than 'reserved' .

Thanks for your comments!

Liang

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[RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast (de)inflating & fast live migration Liang Li <liang.z.li@intel.com> - 2016-10-21 08:40 +0200
  [RESEND PATCH v3 kernel 4/7] virtio-balloon: speed up inflate/deflate process Liang Li <liang.z.li@intel.com> - 2016-10-21 08:40 +0200
    Re: [RESEND PATCH v3 kernel 4/7] virtio-balloon: speed up  inflate/deflate process "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-25 08:40 +0200
      RE: [RESEND PATCH v3 kernel 4/7] virtio-balloon: speed up  inflate/deflate process "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-25 11:50 +0200
  [RESEND PATCH v3 kernel 2/7] virtio-balloon: define new feature bit and page bitmap head Liang Li <liang.z.li@intel.com> - 2016-10-21 08:40 +0200
    Re: [RESEND PATCH v3 kernel 2/7] virtio-balloon: define new feature  bit and page bitmap head Dave Hansen <dave.hansen@intel.com> - 2016-10-24 19:00 +0200
      RE: [RESEND PATCH v3 kernel 2/7] virtio-balloon: define new feature  bit and page bitmap head "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-25 03:30 +0200
    Re: [RESEND PATCH v3 kernel 2/7] virtio-balloon: define new feature  bit and page bitmap head "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-26 17:50 +0200
  [RESEND PATCH v3 kernel 1/7] virtio-balloon: rework deflate to add page to a list Liang Li <liang.z.li@intel.com> - 2016-10-21 08:40 +0200
    Re: [RESEND PATCH v3 kernel 1/7] virtio-balloon: rework deflate to  add page to a list Dave Hansen <dave.hansen@intel.com> - 2016-10-24 18:50 +0200
      RE: [RESEND PATCH v3 kernel 1/7] virtio-balloon: rework deflate to  add page to a list "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-25 03:20 +0200
  Re: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-10-21 19:30 +0200
    Re: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-21 21:50 +0200
      RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-23 13:30 +0200
        Re: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-25 06:00 +0200
    RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-26 12:10 +0200
      RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-26 12:20 +0200
        Re: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-10-26 20:20 +0200
          RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-27 02:40 +0200
      Re: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-10-26 20:20 +0200
        RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-10-27 03:00 +0200

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