[libvirt] [PATCH] qemu: New XML to disable memory merge at guest startup

[Osier Yang]

On 25/04/13 22:14, Eric Blake wrote:
> On 04/17/2013 08:54 AM, Eric Blake wrote:
>> On 04/17/2013 08:22 AM, Osier Yang wrote:
>>> QEMU introduced command line "-mem-merge=on|off" (defaults to on) to
>>> enable/disable the memory merge (KSM) at guest startup. This exposes
>>> it by new XML:
>>>    <memoryBacking>
>>>      <nosharepages/>
>>>    </memoryBacking>
>>>
>>> The XML tag is same with what we used internally for old RHEL.
>> Good - that means that RHEL 6 (and any other downstream distro that was
>> already borrowing the RHEL extension) will not break when rebasing to
>> pick up this change from upstream in place of their downstream extension
>> (RHEL will actually want to add a followup patch on top of this that
>> _also_ tries the older -redhat-disable-KSM downstream spelling of the
>> option, but that's a problem for RHEL and not this list).
>>
>>>   
>>> +    if (strstr(help, "-mem-merge"))
>>> +        virQEMUCapsSet(qemuCaps, QEMU_CAPS_MEM_MERGE);
>> This would only scrape the existence of -mem-merge in qemu 1.2 and
>> earlier, since we don't read -help in 1.3 and later.  But qemu 1.2
>> doesn't have -mem-merge, so this bit will never get set.  You need to
>> instead populate the new capability based on a QMP probe, not string
>> scraping.  But I don't know offhand what that probe would be; you may
>> need to ask on the qemu list.
> And we have a winner.  We are getting query-command-line-options for
> qemu 1.5, and it looks easy enough that distros may be able to backport
> it into earlier qemu (again, I'll leave it up to Red Hat internal lists
> on whether it will be backported to RHEL).
>
> https://lists.gnu.org/archive/html/qemu-devel/2013-04/msg05040.html
>
>> Looking forward to v2.
> Do you need help writing the src/qemu/qemu_monitor_json.c changes needed
> to utilize the new query-command-line-options QMP command, since I kind
> of spearheaded the design review on the qemu list?
>
I don't have much time before the beginning of May.  Appreciated if
you can do it. Or I can take it if it's delayed. :-)

Regards,
Osier