Re: a ton of kernel issues

[George Shuklin <george.shuklin@gmail.com>]

On 13.12.2011 18:18, Konrad Rzeszutek Wilk wrote:

>>> what glitches should one expect with 3.0+, and having the choice,
>>> would it be better to go with 3.1 or even 3.2?
>>>
>> Right now I know about two of them:
>> When you set up memory for virtual machine using xenballon, value in
>> dom0 differ from value in domU. The issue is that -xen kernels 'hide'
>> some memory in 'used' memory, and pv-ops just reducing TotalMem to value
>> without that memory. Practically that means if you set up memory for
>> domain to 2GiB client will saw only 1.95GiB and so on.
>>
>> The second issue is lack of support of 'pre-inflated balloon', means you
>> can not set up memory-static-max to 2GiB, target to 1GiB and do 'memory
>> grow' from 1 G to 2 G latter without VM reboot. -xen kernels allow this
>> (up to memory-static-max limit).
> Is all of this with 'xm' or with 'xl' tools? What happens when you 'grow'
> the memory from 1G to 2G? Are you using the hotplug memory balloon or
> the older one?
This is xcp (with shutdowned squeezed, it not a problem), so we using 
direct calls to xc (domain_set_maxkb), but I can repeat this with xl 
(which one and only one available in XCP), with same results. If I 
create VM with static-max 2GiB, dynamic-max 1GiB, boot it, then:

1) with PV_ops I can go lower than 1GiB, but never any higher than 1GiB
2) with -xen kernels I can go upper to 2GiB.

If I compile kernel with xenballoon hotplug option enabled, after some 
(very small) memory growth (within preallocated memory?) after future 
attempts I getting this message:

[1935380.223401] System RAM resource 18000000 - 27ffffff cannot be added
[1935380.223414] xen_balloon: reserve_additional_memory: add_memory() 
failed: -17

(tested with vanilla 3.0, 3.1 and some RCs of 3.2)