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From: | zhanghailiang |
Subject: | Re: [Qemu-devel] [PATCH v2 1/3] pc-dimm: add a function to calculate VM's current RAM size |
Date: | Thu, 20 Nov 2014 10:31:01 +0800 |
User-agent: | Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Thunderbird/31.1.1 |
On 2014/11/20 0:31, Eric Blake wrote:
On 11/19/2014 09:06 AM, Michael S. Tsirkin wrote:This affects QMP right?I think later patches will tell how. CC'ing Eric.As far as I can tell, this is just correcting a reporting issue; the existing QMP commands/events for tracking balloon size will now properly account for hotplugged memory. What I don't know is if this change in semantics will affect any users. Libvirt is not yet supporting memory hotplug, so ideally, fixing this bug before libvirt uses memory hotplug means libvirt will never have to worry about qemu versions that do incorrect reporting. The alternative is to declare that the existing QMP commands cannot change in semantics for the existing members that it reports, and must instead report additional dictionary members describing the amount of hot-plugged memory, and then require that the client add the numbers together itself. That sounds mean to the client, so I'm hoping we don't have to go there.IOW you ack this patch for 2.2?Is memory hotplug one of the new features in 2.2? If so, then yes, we
No, after searching this feature in ChangeLogs, i found pc-dimm memory hotplug was supported since 2.1. It only supports for x86 target. And one more thing, i found in 2.2's Changelog it begin to support memory hotplug for s390 target, I'm not sure whether this problem also exists for s390.
should get its semantics right from the start (this is a bug fix to avoid a release with broken semantics). On the other hand, if hotplug existed in 2.1, then we already have a release with odd semantics, so delaying this fix until 2.3 and leaving 2.2 with the same odd semantics would not hurt, and it then becomes a judgment call of whether we are rushing in a possibly incomplete solution by trying to get this into 2.2. (Sorry I haven't been following the history of memory hotplug closer)
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