Re: [Xen-devel] a ton of kernel issues

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Wed, Dec 14, 2011 at 01:10:39AM +0400, George Shuklin wrote:
> 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

I just tried this, and had these two options in my guest config:

maxmem=2048
mem=1024

booted up the guest and from dom0 did "xm mem-set latest 2048"
and it expanded to 2G. Did "xm mem-set latest 10248" and it went down.

Is this how you are doing it as well? (I have to confess I don't know
much about XCP so don't know if those 'static-max, dynamic-max'
are the same thing).

Is this PV bootup? Or HVM?

> 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

Hm, that looks like a bug. But the old style balloon code does work.
Not sure why with a default .config you are hitting these issues.
> 
> (tested with vanilla 3.0, 3.1 and some RCs of 3.2)
> 
> 
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