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


  • To: Hans van Kranenburg <hans@xxxxxxxxxxx>, "Durrant, Paul" <pdurrant@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>
  • From: George Dunlap <george.dunlap@xxxxxxxxxx>
  • Date: Thu, 28 Nov 2019 14:54:30 +0000
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 28 Nov 2019 14:54:37 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 11/27/19 10:32 PM, 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.

This rather suggests that the default value isn't very well chosen.
Ideally some investigation would be done to improve the default sizing;
end-users shouldn't have to know anything about grant table frames.

 -George

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