[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] PoD, 4.2, and current/maximum reservation



>>> On 11.02.13 at 12:40, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 11/02/13 11:39, James Harper wrote:
>>> On Mon, Feb 11, 2013 at 12:03 AM, James Harper
>>> <james.harper@xxxxxxxxxxxxxxxx> wrote:
>>>
>>>     A user has pointed out a problem with GPLPV under Xen 4.2 when
>>> using PoD. I'm using the difference between
>>> XENMEM_maximum_reservation and XENMEM_current_reservation to tell
>>> me how much I should balloon down to account for PoD, but when the user
>>> has ballooned down to 1G (from 4Gb or 8GB), GPLPV logs the following:
>>>
>>>     13005008825593: XenPCI     XENMEM_maximum_reservation =
>>> 262400
>>>     13005008825593: XenPCI     XENMEM_current_reservation = 262136
>>>     13005008825609: XenPCI     Trying to give 1056 KB (1 MB) to Xen
>>>
>>>     What is the correct way to tell how much PoD memory there is under
>>> 4.2? Am I doing it wrong?
>>>
>>>     I balloon down as early as possible (before xenbus starts) to avoid
>>> windows going over its limit so I'm hoping I can determine the size of PoD
>>> memory just via hypercalls.
>>>
>>>
>>>
>>> You shouldn't have to know anything specifically about PoD -- you should 
>>> just
>>> look at the balloon target for the guest written in xenstore.  The idea was 
> as
>>> much as possible for the toolstack and Xen to work together to make it
>>> transparent to the balloon driver, in part because we expected to be running
>>> legacy drivers.  The Citrix PV drivers don't do anything special wrt PoD
>>> memory.  (Paul, please correct me if I'm wrong.)
>> So I should just balloon down to the current_reservation figure right?
> 
> ...I don't think so -- it looks like you're getting that from a 
> hypercall, not from xenstore.  You want the normal balloon target value 
> from xenstore.  (But I might be confused -- I'm not super familiar with 
> the technical details of the ballooning codepath, just the overall 
> principles.)

As James said, this ought to run without xenbus having initialized
(so it can be done as early as possible). Hence the need for doing
this via hypercalls. The "classic" Xen balloon driver does so too, btw.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.