Re: [Qemu-devel] mem1 is in use, can not be deleted

[Eduardo Otubo <eduardo.otubo@profitbricks.com>]

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On Tue, Jun 30, 2015 at 05=56=02PM +0200, Igor Mammedov wrote:
> On Tue, 30 Jun 2015 15:56:13 +0200
> Eduardo Otubo <eduardo.otubo@profitbricks.com> wrote:
> 
> > On Tue, Jun 30, 2015 at 11=18=21AM +0200, Igor Mammedov wrote:
> > > On Tue, 30 Jun 2015 10:07:52 +0200
> > > Eduardo Otubo <eduardo.otubo@profitbricks.com> wrote:
> > > 
> > > > Hello all,
> > > > 
> > > > I compiled the HEAD of the master branch and was testing memory
> > > > hotunplug and got to this issue. Note: I followed exactly what's
> > > > written on the docs/memory-hotplug.txt file.
> > > > 
> > > > QEMU 2.3.50 monitor - type 'help' for more information
> > > > (qemu) object_add memory-backend-ram,id=mem1,size=1G
> > > > object_add memory-backend-ram,id=mem1,size=1G
> > > > (qemu) device_add pc-dimm,id=dimm1,memdev=mem1
> > > > device_add pc-dimm,id=dimm1,memdev=mem1
> > > > (qemu) device_del dimm1
> > > > device_del dimm1
> > > > (qemu) object_del mem1
> > > > object_del mem1
> > > > mem1 is in use, can not be deleted
> > > 
> > > probably because  dimm1 isn't deleted,
> > > you can check it in monitor using command "info memory-devices"
> > 
> > Yes, you're right. The reason is surely because dimm1 wasn't deleted
> > -- and I think I didn't make my point very clear -- my question was
> > more about: Is there any reason for dimm1 not being deleted? The
> > reason why I tested with the guest OS fully running and on GRUB is
> > because I guessed the guest OS was using this memory and couldn't be
> > deallocated. If that's the case, and qemu did a best effort to remove
> > and couldn't because guest was using it, then Ok, I just need to
> > adapt my tests. Other than that perhaps I hit a bug.
> Guest OS has to:
>  1. support memory hot remove

How do I know if guest OS supports memory hot remove? I'm testing on
Debian 8 with kernel 4.1. I start qemu with "-m 2G,slots=32,maxmem=8G".

>  2. eject memory device using ACPI _EJ0 method, once it has handled
>  removal request, provided it is able to free corresponding memory pages
> See docs they should have flows described for success and failure case.

When I issue the command "device_del dimm1" I see no output on dmesg on
the guest OS. I guess this is a sign that perhaps the guest does not
support it?

From the (very nice) diagram I found at docs/specs/acpi_mem_hotplug.txt,
Qemu QMP should output some sort of failure if Guest OS fails to
process ejection right? The only information I see is:

 (qemu) device_del dimm1
 device_del dimm1

 (qemu) info memory-devices
 info memory-devices
 Memory device [dimm]: "dimm1"
   addr: 0x100000000
   slot: 0
   node: 0
   size: 1073741824
   memdev: /objects/mem1
   hotplugged: true
   hotpluggable: true

 (qemu) info memdev
 info memdev
 memory backend: 0
   size:  1073741824
   merge: true
   dump: true
   prealloc: false
   policy: default
   host nodes: 

How was the environment when you tested this feature?

Regards,

-- 
Eduardo Otubo
ProfitBricks GmbH

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