Re: null domains | xen4.4

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2014-12-01 at 12:48 +0300, Alexey wrote:
> Hi, all!
> 
> We are once again faced with the null-domains problem.
> At this moment we have xen node with 49 null-domains and if I create new 
> domain and shutdown it I w'll get a new one null-domain.
> 
> All blkback and netback kernel process are exists. There is no qemu 
> process running.
> I can't delete any vif or stop disk, which was used by dead domain.

What do you mean here, does a vif or disk still exist for the dead
domain then?

> How we can prevent appearance of null-domains?
> How we can unlock resources of existing null-domains?

A null domain remains when a page owned by that domain is still
referenced from somewhere. The output of the 'q' debug key sometimes
exposes the source of such references. ("xl debug-key q" will send that,
the result appears in "xl dmesg", alternatively Ctrl-A three times on
the serial console then 'q').

> # xl info
> host                   : xen23
> release                : 3.10-3-amd64

Any chance you could try a newer dom0 kernel?

> xen_commandline        : tmem=1 loglvl=all noreboot dom0_mem=5120M 
> dom0_vcpus_pin console=vga vga=current

Are you able to reproduce when tmem is not enabled?

Ian.