RE: [Xen-devel] [PATCH] Fix restore handling checks

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Correct me if I am wrong, but I think your patch assumes
that the amount of free memory in the system can be
computed by assuming each guest memory is fixed size.
Due to various features in Xen 4.0, this is no longer
a safe assumption.  Tmem has a libxc call to freeze
and unfreeze its use of memory so dynamic memory use
by tmem can be stopped, and another libxc call to
determine "freeable" memory, and another to free it.
I don't know if the page-sharing functionality added
at 4.0 has anything similar.

But in any case, simple algorithms to add up current
(or max) guest memory will have many false-positive
and false-negative results.

> -----Original Message-----
> From: Michal Novotny [mailto:minovotn@xxxxxxxxxx]
> Sent: Tuesday, June 22, 2010 6:56 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH] Fix restore handling checks
> 
> On 06/22/2010 08:17 AM, Michal Novotny wrote:
> > On 06/22/2010 08:14 AM, Keir Fraser wrote:
> >> Okay, hopefully someone will be able to Ack this patch with better
> >> knwoledge
> >> of xend than me.
> >>
> >>   -- Keir
> >>
> > Ok, good. If it will be accepted and put into xen-staging/xen-
> unstable
> > tree please let me know about it.
> >
> > Thanks,
> > Michal
> >
> 
> Well, this is new version of the patch since I've tried now to both
> migrate from RHEL-5 host (python-2.4) to RHEL-6 host (python-2.6) using
> the RHEL-5 host as a source machine for migrations and also RHEL-6 host
> to restore the the guest locally using `xm restore` to see whether the
> guest memory calculated correctly and it did pass when there was enough
> memory to create the guest and failed when there was not enough memory
> to create the guest. Also, some fixing for comparing the values was
> necessary since it was treated as string comparison on one of the
> hosts.
> 
> Both the host machines were having the latest Xen-4.1 installed.
> 
> Michal
> 
> Signed-off-by: Michal Novotny <minovotn@xxxxxxxxxx>
> 
> --
> Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
> Virtualization Team (xen userspace), Red Hat
> 

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