Re: save & restore failed when tmem enabled in Xen 4.1 & Xen 4.3

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/06/15 19:45, Konrad Rzeszutek Wilk wrote:
> On Thu, Jun 04, 2015 at 10:27:06PM +0800, yunfang tai wrote:
>> Hi all,
> Hey!
>>     Recently, I am testing the TMEM support on Xen. I discovered that when
>> enabled TMEM in ubuntu 14.10 as guest on Xen 4.1 & Xen 4.3, "xm save" & "xm
>> restore“ failed after there are more than 1000 pages put in persistent pool
>> of TMEM in Xen. My operations are list as follows:
> Is it exactly 1000 or just about? I presume it does not matter how much but
> that you discovered it by having 1000 of them?
>
>> In ubuntu guest (8 cores , 8GB):
>> sudo modprobe tmem
>> (than wait for the selfballoon to finish)
>> dd if=/dev/zero of=/tmp/test.img bs=10M count=1000
>> dd if=/tmp/test.img of=/dev/null bs=10M
>> dd if=/tmp/test.img of=/dev/null bs=10M
>> .........
>> (until more than 1000 pages put in persistent pool)
>> In Domain 0:
>> (add tmem in grub.cfg)
>> xm save ubuntu test.save
>> xm restore ubuntu test.save
>>
>> When TMEM is not enabled, save & restore success after these operations.
>> But if TMEM is enabled, save & restore fail.
> Are there any errors from the logs? Anything?
>> Does anyone test about save & restore when enabled TMEM in Xen?? Is there
>> anything I do wrong?
> Well lets see what broke. But I think Andrew discovered that the
> migration protocol when it came to 'tmem' was not up to snuff. CC-ing him
> just to confirm.
>
> (Andrew, for the persistent part of this - it conceptually should
> get all of the tmem memory that pushed to the hypervisor back in the
> image. When you were looking at migrationv2 did you just skim through
> that or mostly ignored it?)

Took a look at the code, attempted to figure out what was going on, then
decided to ignore it for the time being.

As a baseline, there is no error checking of hypercalls or their
returned data putting the data into the stream.

Migration v2 currently has no TMEM support, and I would suggest
re-implementing it from scratch over attempting to port what currently
exists for legacy.

~Andrew

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