Re: [virtio-dev] [PATCH v8 1/3] content: Document balloon feature free page hints

[Jan Kiszka <jan.kiszka@siemens.com>]

On 25.08.20 16:45, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
> Free page hints allow the balloon driver to provide information on what
> pages are not currently in use so that we can avoid the cost of copying
> them in migration scenarios. Add a feature description for free page hints
> describing basic functioning and requirements.
> 
> Acked-by: Cornelia Huck <cohuck@redhat.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> ---
>  conformance.tex |    2 +
>  content.tex     |  161 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 157 insertions(+), 6 deletions(-)
> 
> diff --git a/conformance.tex b/conformance.tex
> index b6fdec090383..a14e26edfcb2 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -149,6 +149,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{drivernormative:Device Types / Memory Balloon Device / Feature bits}
>  \item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation}
>  \item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation / Memory Statistics}
> +\item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation / Free Page Hinting}
>  \end{itemize}
>  
>  \conformance{\subsection}{SCSI Host Driver Conformance}\label{sec:Conformance / Driver Conformance / SCSI Host Driver Conformance}
> @@ -331,6 +332,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{devicenormative:Device Types / Memory Balloon Device / Feature bits}
>  \item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation}
>  \item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation / Memory Statistics}
> +\item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation / Free Page Hinting}
>  \end{itemize}
>  
>  \conformance{\subsection}{SCSI Host Device Conformance}\label{sec:Conformance / Device Conformance / SCSI Host Device Conformance}
> diff --git a/content.tex b/content.tex
> index 91735e3eb018..76dfce919b97 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -5005,10 +5005,13 @@ \subsection{Virtqueues}\label{sec:Device Types / Memory Balloon Device / Virtque
>  \begin{description}
>  \item[0] inflateq
>  \item[1] deflateq
> -\item[2] statsq.
> +\item[2] statsq
> +\item[3] free_page_vq
>  \end{description}
>  
> -  Virtqueue 2 only exists if VIRTIO_BALLOON_F_STATS_VQ set.
> +  statsq only exists if VIRTIO_BALLOON_F_STATS_VQ is set.
> +
> +  free_page_vq only exists if VIRTIO_BALLOON_F_FREE_PAGE_HINT is set.
>  
>  \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Feature bits}
>  \begin{description}
> @@ -5019,6 +5022,10 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Featu
>      memory statistics is present.
>  \item[VIRTIO_BALLOON_F_DEFLATE_ON_OOM (2) ] Deflate balloon on
>      guest out of memory condition.
> +\item[ VIRTIO_BALLOON_F_FREE_PAGE_HINT(3) ] The device has support for free
> +    page hinting. A virtqueue for providing hints as to what memory is
> +    currently free is present. Configuration field \field{free_page_hint_cmd_id}
> +    is valid.
>  
>  \end{description}
>  
> @@ -5042,13 +5049,17 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Featu
>  VIRTIO_BALLOON_F_MUST_TELL_HOST is not negotiated.
>  
>  \subsection{Device configuration layout}\label{sec:Device Types / Memory Balloon Device / Device configuration layout}
> -  Both fields of this configuration
> -  are always available.
> +  \field{num_pages} and \field{actual} are always available.
> +
> +  \field{free_page_hint_cmd_id} is available if
> +    VIRTIO_BALLOON_F_FREE_PAGE_HINT has been negotiated and is read-only by
> +    the driver.

This reads at least to me like "...if VIRTIO_BALLOON_F_FREE_PAGE_HINT
... is read-only by the driver". I suspect you rather meant
"free_page_hint_cmd_id is read-only...". Maybe split up into two sentences?

Jan

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