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

[Marco Guazzone <marco.guazzone@xxxxxxxxx>]

Hi Ian,

Thanks for your reply

On Mon, Oct 12, 2015 at 12:02 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> On Mon, 2015-10-12 at 11:10 +0200, Marco Guazzone wrote:

[big cut]

>> Your suggestions are clear to me, but I still don't understand the
>> purpose "xl mem-max" command. :-)
>
> It allows the hotplugging of additional memory banks.
>
> When starting a guest with memory=X + maxmem=Y (where X<=Y) you can use "xl
> mem-set" to balloon the guest up to a maximum of Y (and a minimum of some
> OS specific minimum). This requires you to have a balloon driver in your
> guest kernel.
>
> If you want to increase to more than Y then you need to use xl mem-max to
> increase the maximum memory to something greater by hotplugging additional
> memory capacity, e.g. Z. Now you can use xl mem-set to balloon the guest up
> to Z. This requires memory hotplug support in your guest in addition to the
> balloon driver.
>

Hmmm. It seems it does not work in my case since I get an ERROR from Xen.
My domain is statically configured with 8GB:
  maxmem = 8192
  memory = 8192

1. Boot:
  memtest                                       45  7935     1
-b----      11.0

2. xl mem-max memtest 10g
  memtest                                       45  7935     1
-b----      11.4

3. 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


It seems that I cannot exceed the statically configured max memory.
Obviously I can assign a lower amout of memory (lower than the
statically configured max value), like 4 GB):
4. xl mem-set  memtest 4g
  memtest                                       45  3839     1
r-----      13.5

I'm still confused.

Best,

Marco

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