Re: [Xen-users] Purpose of mem-max command

[Marco Guazzone <marco.guazzone@xxxxxxxxx>]

On Mon, Oct 12, 2015 at 7:45 PM, Simon Hobson <linux@xxxxxxxxxxxxxxxx> wrote:
> Marco Guazzone <marco.guazzone@xxxxxxxxx> wrote:
>
>> Hmmm. It seems it does not work in my case since I get an ERROR from Xen.
>
> Does your guest OS support memory hotplug ?
> As described by others, if your guest does not support memory hotplug, then 
> you can only ballon guest memory up to the amount specified as max-mem at 
> startup time. Only if you have hotplug support can you "hot plug" extra 
> memory into the guest system over and above what was configured as max-mem at 
> startup time.
>

My host system:
- Fedora Linux 21 x86_64
- kernel: 4.1.8-100
- Xen: 4.4.3-4

My guest system:
- CentOS Linux 7.1.1503 (Core)  x86_64
- kernel: 3.10.0-229.14.1

I think the guest OS support mem hotplug since I can see the related
sysfs files in /sys/devices/system/memory/.
For instance:
$ grep -r --include="state" "line" /sys/devices/system/memory/
/sys/devices/system/memory/memory0/state:online
/sys/devices/system/memory/memory1/state:online
/sys/devices/system/memory/memory2/state:online
/sys/devices/system/memory/memory3/state:online
...
/sys/devices/system/memory/memory65/state:online

But if you know any other practical check, please tell me.

Meanwhile, I've tried  to increase RAM again, from 8g to 10g:
$ xl mem-max memtest 10g

Then I've checked if something is changed in sysfs (the hope was at
least to see new memory marked as offline).
But nothing has changed. I see tha same memory banks (from 0 to 65)
And if I try to set 9GB of RAM I got the same error as before:
$ xl mem-set memtest 9g
libxl: error: libxl.c:4104:libxl_set_memory_target: memory_dynamic_max
must be less than or equal to memory_static_max

If you know a linux distribution where hotplug works for sure I can
try to create a VM with that OS

Thank you so much.

Marco

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