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

[Eduardo Otubo]

> > > > 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".
> kernel should be compiled with memory remove options

Double checked that and yes, my guest kernel has memory hotplug support.

> 
> Also memory removal is allowed to fail if guest kernel is not able
> to offline corresponding memory sections but it probably should notify
> QEMU via ACPI about failure.

How can I check this notification?

> 
> 
> > 
> > >  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:
> you need to use query-acpi-ospm-status command to see slot status.

Yep, this command outputs that the dimm is still there, no news :/

> 
> > 
> >  (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?
> Most likely I've used RHEL7.1 as guest with latest systemd
> which onlines hotplugged memory automatically on hotplug.

I tried with Ubuntu 15.04, latest kernel 4.2 and systemd, still not
working. I'm downloading CentOS-7, I'll setup with systemd and proper
kernel configuration. I'll let you know the results.

Thanks a lot for the help so far! :)

-- 
Eduardo Otubo
ProfitBricks GmbH

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