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Subject: Re: [virtio-comment] [PATCH v2 1/3] content: Document balloon feature free page hints
On Mon, 18 May 2020 13:15:50 -0700 Alexander Duyck <alexander.duyck@gmail.com> wrote: > On Mon, May 18, 2020 at 6:18 AM David Hildenbrand <david@redhat.com> wrote: > > > > On 15.05.20 19:33, Alexander Duyck wrote: > > > +\subsubsection{Free Page Hinting}\label{sec:Device Types / Memory Balloon Device / Device Operation / Free Page Hinting} > > > + > > > +Free page hinting is designed to be used during migration to determine what > > > +pages within the guest are currently unused so that they can be skipped over > > > +while migrating the guest. The device will indicate that it is ready to start > > > +performing hinting by setting the \field{free_page_hint_cmd_id} to one of the > > > +non-reserved values that can be used as a command ID. The following values > > > +are reserved: > > > + > > > +\begin{description} > > > +\item[VIRTIO_BALLOON_CMD_ID_STOP (0)] Any command ID previously supplied by > > > + the device is invalid. The driver should halt all hinting until a new > > > + command ID is supplied. > > > > Maybe "The driver should stop hinting free pages, but should not reuse > > all previously hinted pages." > > The "reuse all previously hinted pages" seems rather unclear to me. I > would like to make clear that in this case the "use" is the guest > making use of the memory, not the driver doing something like > recycling hints. So in the spots where you reference "the driver > reusing pages" I think I might prefer to go with something along the > lines of "releasing pages for use by the guest". The problem is that > when you have a balloon we were referencing using pages from the > balloon. Since we cannot reference the balloon I figure I will go with > language where we "supply" and "release" hinted pages. That way we > acknowledge that the driver is holding onto pages and not freeing them > for use by the guest. > > I'll probably go with something like: > The driver should stop hinting free pages, but > should not release any hinted pages for use by the guest. "The driver should stop hinting free pages until a new command ID is supplied, but should not release..." would sound good to me. > > > > + > > > +\item[VIRTIO_BALLOON_CMD_ID_DONE (1)] Any command ID previously supplied by > > > + the device is invalid. The driver should halt all hinting and the hinting > > > + balloon can now be deflated returning all pages to the guest. > > > > I would avoid the terminology "hinting balloon" and "deflation". > > So I will clean up the spots you pointed out and also work on the > workflow down below that includes "hinting balloon" in the > terminology. > > > "The driver should stop hinting free pages and should reuse all > > previously hinted pages.". > > Similar to the comment above: > The driver should stop hinting free pages, and > should release all hinted pages for use by the guest. Also sounds good to me.
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