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Subject: Re: [PATCH v1 1/2] content/virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT
On 01/15/2019 02:58 AM, Michael S. Tsirkin wrote:
On Tue, Nov 13, 2018 at 06:27:46PM +0800, Wei Wang wrote:+\field{num_pages} and \field{actual} are always available.+ +\field{free_page_report_cmd_id} is available if +VIRTIO_BALLON_F_FREE_PAGE_HINT negotiated. + +\devicenormative{\subsubsection}{Device configuration layout}{Device Types / Traditional Memory Balloon Device / Device configuration layout} + +The device MUST NOT set \field{free_page_report_cmd_id} to a value +between \field{VIRTIO_BALLOON_CMD_ID_DONE} and +\field{VIRTIO_BALLOON_CMD_ID_MIN} exclusive. Exclusive is confusing since you can include one edge or both. Let's write it up positively. So the only legal values are VIRTIO_BALLOON_CMD_ID_MIN to VIRTIO_BALLOON_CMD_ID_MAX inclusive or VIRTIO_BALLOON_CMD_ID_STOP?
OK, plan to change it:
The device MUST set a legal value to \field{free_page_report_cmd_id}:
a value between \field{VIRTIO_BALLOON_CMD_ID_MIN} and
\field{VIRTIO_BALLOON_CMD_ID_MAX} inclusive,
\field{VIRTIO_BALLOON_CMD_ID_STOP}, or
\field{VIRTIO_BALLOON_CMD_ID_DONE}.
+ \subparagraph{Legacy Interface: Device configuration layout}\label{sec:Device Types / Memory Balloon Device / Device configuration layout / Legacy Interface: Device configuration layout} When using the legacy interface, transitional devices and drivers @@ -4448,8 +4469,20 @@ The device initialization process is outlined below: \item DRIVER_OK is set: device operation begins. \item Notify the device about the stats virtqueue buffer. \end{enumerate} + +\item If the VIRTIO_BALLOON_F_FREE_PAGE_HINT feature bit is + negotiated: + \begin{enumerate} + \item Identify the free page virtqueue. + \item Set \field{free_page_report_cmd_id} to + \field{VIRTIO_BALLOON_CMD_ID_MIN}.Does driver does it or the device? And does it have to be MIN? Why? Should not driver *read* the ID instead?
Yes, the device sets the value and the driver reads it. Probably not necessarily have to be MIN.
Plan to change:
\item If the VIRTIO_BALLOON_F_FREE_PAGE_HINT feature bit is
negotiated:
\begin{enumerate}
\item Identify the free page virtqueue.
\item Set \field{free_page_report_cmd_id} to a legal value.
\end{enumerate}
+ \item Register a notifier with an external component (e.g. a live + migration agent) who will request for the free page reporting + from the driver.Spec only operates in terms of driver and device. I don't know what does above mean in these terms but please restate it accordingly. No notifiers live migration agents and external (to what?) components please.
OK, removed this part.
+\item The driver reads \field{free_page_report_cmd_id}: if it is not + \field{VIRTIO_BALLOON_CMD_ID_STOP}, + \field{VIRTIO_BALLOON_CMD_ID_DONE}, and different from the value it + read last time, start free page reporting as follows: + \begin{enumerate} + \item Write the received \field{free_page_report_cmd_id} to a + buffer and add it to the free page virtqueue to indicate the start + of the reporting. + \item Collect free pages and write each page address into an entry + of the virtqueue.Spec does not define terms such as entry for virtqueue or writing into virtqueue. What you mean is add each page as an input buffer to the virtqueue I think? Also are there any alignment assumptions? What does "page" mean here generally? A size aligned physically contigious region of free memory?
OK, thanks for your suggestions.
Here is the rewording (changed page to memory):
\begin{enumerate}
\item The device updates \field{free_page_report_cmd_id}: if it has
reached \field{VIRTIO_BALLOON_CMD_ID_MAX}, resets it to
\field{VIRTIO_BALLOON_CMD_ID_MIN}. Otherwise, increments it by 1.
\item The device sends a configuration change notification to the
driver.
\item The driver reads \field{free_page_report_cmd_id}: if it is not
\field{VIRTIO_BALLOON_CMD_ID_STOP},
\field{VIRTIO_BALLOON_CMD_ID_DONE}, and different from the value it
read last time, start free page reporting as follows:
\begin{enumerate}
\item Write the received \field{free_page_report_cmd_id} to a
buffer from the free page virtqueue.
\item Write addresses of guest free memory to buffers from the free
page virtqueue.
\item Write \field{VIRTIO_BALLOON_CMD_ID_STOP} to a buffer from the
free page virtqueue, which signifies that the guest free memory
reporting is complete.
\end{enumerate}
A driver to device notification is sent in the above steps after
writing a buffer from the free page virtqueue if the notification
is not suppressed.
\item The device processes available buffers from the virtqueue and
stops the processing after it reads a buffer which stores
\field{VIRTIO_BALLOON_CMD_ID_STOP}.
\end{enumerate}
A request to actively stop the free page reporting proceeds as
follows:
\begin{enumerate}
\item The device sets \field{free_page_report_cmd_id} to
\field{VIRTIO_BALLOON_CMD_ID_STOP}, followed by a configuration
change notification to the driver if not suppressed.
\item The driver reads \field{free_page_report_cmd_id} and identifies
that it is \field{VIRTIO_BALLOON_CMD_ID_STOP}, then it stops
adding buffers to the free page virtqueue.
\item The driver writes \field{VIRTIO_BALLOON_CMD_ID_STOP} into a
buffer from virtqueue.
\item The device stops processing the available buffers from the
virtqueue after receiving the buffer that stores
\field{VIRTIO_BALLOON_CMD_ID_STOP}.
\end{enumerate}
The device can end the free page reporting by setting
\field{free_page_report_cmd_id} to \field{VIRTIO_BALLOON_CMD_ID_DONE},
followed by a configuration notification to the driver.
+ +The driver SHOULD add the addresses of free pages as input buffers +to the virtqueue. + +The driver SHOULD add the buffer that stores the value of +\field{free_page_report_cmd_id} or \field{VIRTIO_BALLOON_CMD_ID_STOP} +as an output buffer to the virtqueue. + +The driver SHOULD use different buffers to send the the value of +\field{free_page_report_cmd_id} and +\field{VIRTIO_BALLOON_CMD_ID_STOP} to avoid one being overwritten by +another when the device has a delay in reading the command. + +The driver SHOULD release all the collected free pages after receiving +\field{VIRTIO_BALLOON_CMD_ID_DONE}. + \section{SCSI Host Device}\label{sec:Device Types / SCSI Host Device}The virtio SCSI host device groups together one or more virtual-- 2.7.4
The above looks like implementation related, I also plan to remove them. Thanks for your comments! Best, Wei
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