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

From: "Jürgen Groß" <jgross@suse.com>
To: Hans van Kranenburg <hans@knorrie.org>,
	"Durrant, Paul" <pdurrant@amazon.com>,
	Ian Jackson <ian.jackson@citrix.com>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
	"Julien Grall" <julien@xen.org>, "Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Andrew Cooper" <Andrew.Cooper3@citrix.com>,
	"Paul Durrant" <paul@xen.org>,
	"George Dunlap" <George.Dunlap@citrix.com>,
	"Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>,
	"Jan Beulich" <jbeulich@suse.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH for-4.13 2/2] Rationalize max_grant_frames and max_maptrack_frames handling
Date: Thu, 28 Nov 2019 06:57:51 +0100	[thread overview]
Message-ID: <8649c91d-7896-283f-75c5-89dc577af7af@suse.com> (raw)
In-Reply-To: <bdbaf3d0-4b78-cbc9-3943-5bc4cfd7cb27@knorrie.org>

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@citrix.com>
>>> 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@lists.xenproject.org> 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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