xl mem-set for domain 0 regression

xl mem-set for domain 0 regression

[James Dingwall]

Hi,

We are migrating from xen 4.4 to xen 4.8.  At the moment we boot our 
system with a xen command line that includes 
"dom0_mem=8192m,min:1728m,max:8192m".  We have autoballoon of dom0 
disabled in xl.conf and instead call xl mem-set 0 <memory_size> to 
change the dom0 memory allocation.  (We shrink before starting guest 
domains and then increase it when all are stopped.)

In xen 4.8.2 the xl mem-set command fails with this error:

# xl mem-set 0 3990
libxl: error: libxl.c:4196:libxl_set_memory_target: unable to retrieve 
domain configuration: No such file or directory
cannot set domid 0 dynamic max memory to : 3990

I think it was the following commit that made it necessary to access the 
configuration file but perhaps for the case domid == 0 this should be 
skipped?  If it is that simple I could try a patch which includes that 
test.

commit 38cd0664a6bf1c3b887992ea029d2bb516f52c59
Author: Shannon Zhao <shannon.zhao@linaro.org>
Date:   Wed Sep 28 18:19:02 2016 -0700

     libxl/arm: Add the size of ACPI tables to maxmem

     Here it adds the ACPI tables size to set the target maxmem to avoid
     providing less available memory for guest.


Thanks,
James

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Re: xl mem-set for domain 0 regression

[Wei Liu]

On Tue, Oct 10, 2017 at 04:03:32PM +0100, James Dingwall wrote:
> Hi,
> 
> We are migrating from xen 4.4 to xen 4.8.  At the moment we boot our system
> with a xen command line that includes "dom0_mem=8192m,min:1728m,max:8192m".
> We have autoballoon of dom0 disabled in xl.conf and instead call xl mem-set
> 0 <memory_size> to change the dom0 memory allocation.  (We shrink before
> starting guest domains and then increase it when all are stopped.)
> 
> In xen 4.8.2 the xl mem-set command fails with this error:
> 
> # xl mem-set 0 3990
> libxl: error: libxl.c:4196:libxl_set_memory_target: unable to retrieve
> domain configuration: No such file or directory
> cannot set domid 0 dynamic max memory to : 3990
> 
> I think it was the following commit that made it necessary to access the
> configuration file but perhaps for the case domid == 0 this should be
> skipped?  If it is that simple I could try a patch which includes that test.

There should be a stub configuration file generated for Dom0.

Check if there is /var/lib/xen/userdata-d.0.0000-*000.libxl-json ?

If not, check if xen-init-dom0 service is run?

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Re: xl mem-set for domain 0 regression

[James Dingwall]

On Wed, Oct 11, 2017 at 05:00:45PM +0100, Wei Liu wrote:
> On Tue, Oct 10, 2017 at 04:03:32PM +0100, James Dingwall wrote:
> > Hi,
> > 
> > We are migrating from xen 4.4 to xen 4.8.  At the moment we boot our system
> > with a xen command line that includes "dom0_mem=8192m,min:1728m,max:8192m".
> > We have autoballoon of dom0 disabled in xl.conf and instead call xl mem-set
> > 0 <memory_size> to change the dom0 memory allocation.  (We shrink before
> > starting guest domains and then increase it when all are stopped.)
> > 
> > In xen 4.8.2 the xl mem-set command fails with this error:
> > 
> > # xl mem-set 0 3990
> > libxl: error: libxl.c:4196:libxl_set_memory_target: unable to retrieve
> > domain configuration: No such file or directory
> > cannot set domid 0 dynamic max memory to : 3990
> > 
> > I think it was the following commit that made it necessary to access the
> > configuration file but perhaps for the case domid == 0 this should be
> > skipped?  If it is that simple I could try a patch which includes that test.
> 
> There should be a stub configuration file generated for Dom0.
> 
> Check if there is /var/lib/xen/userdata-d.0.0000-*000.libxl-json ?
> 
> If not, check if xen-init-dom0 service is run?

Ahh... :) That was exactly the issue.  We are not using the default startup scripts so this was not called.  I 
had compared to a Gentoo system where this file was not present (for exactly the same reason).  I shall pay more 
attention to the default scripts to ensure there is nothing else we have missed.

Thanks,

James

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