Re: [Xen-devel] [PATCH for-4.13 2/2] Rationalize max_grant_frames and max_maptrack_frames handling

[Jürgen Groß <jgross@xxxxxxxx>]

On 27.11.19 23:32, Hans van Kranenburg wrote:
> Hi all,
>
> On 11/27/19 12:13 PM, Durrant, Paul wrote:
> > > -----Original Message-----
> > > From: Ian Jackson <ian.jackson@xxxxxxxxxx>
> > > Sent: 27 November 2019 11:10
> > > [...]
> > > Subject: RE: [Xen-devel] [PATCH for-4.13 2/2] Rationalize max_grant_frames
> > > and max_maptrack_frames handling
> > >
> > > Durrant, Paul writes ("RE: [Xen-devel] [PATCH for-4.13 2/2] Rationalize
> > > max_grant_frames and max_maptrack_frames handling"):
> > > > > -----Original Message-----
> > > > > From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of
> > > Ian
> > > > > Jackson
> > > > > I have seen reports of users who ran out of grant/maptrack frames
> > > > > because of updates to use multiring protocols etc.  The error messages
> > > > > are not very good and the recommended workaround has been to increase
> > > > > the default limit on the hypervisor command line.
> > > > >
> > > > > It is important that we don't break that workaround!
> > > > Alas it has apparently been broken for several releases now :-(
> > > I guess at least in Debian (where I have seen this) we haven't
> > > released with any affected versions yet...
> > I believe the problem was introduce in 4.10, so I think it would be prudent to 
> > also back-port the final fix to stable trees from then on.
> Yes, the max grant frame issue has historically always been a painful
> experience for end users, and Xen 4.11 which we now have in the current
> Debian stable has made it worse compared to previous versions indeed.
>
> Changing the hypervisor command line worked in the past, and now that
> value is overwritten again by a lower value in the toolstack, which
> requires setting per-domU settings, or, what I did, just additionally
> also setting max_grant_frames in /etc/xen/xl.conf to the same value as
> the hypervisor command line.
>
> This change is very welcome, even to 4.11-stable if possible, since it
> will not break existing configuration of users.
>
> If changing only the value of the hypervisor command line works again,
> then old information that shows up when the users searches the web will
> be useful again, which is good.
>
> Hans
>
> P.S. Now I'm curious to figure out what a maptrack frame is, didn't hear
> about that one before.
The maptrack frames are used by the hypervisor for keeping track which
grants are mapped by a specific domain. So they are necessary for driver
domains (including dom0), and max_maptrack_frames limits how many
mappings of other domain's pages can be active simultaneously in a
domain.


Juergen

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