Re: [Qemu-devel] [RFC PATCH v4 00/30] ACPI memory hotplug

[li guang]

在 2013-03-26二的 17:43 +0100，Vasilis Liaskovitis写道：
> Hi,
> 
> On Tue, Mar 19, 2013 at 03:28:38PM +0800, li guang wrote:
> [...]
> > > > > This is v4 of the ACPI memory hotplug functionality. Only x86_64 
> > > > > target is
> > > > > supported (both i440fx and q35). There are still several issues, but 
> > > > > it's
> > > > > been a while since v3 and I wanted to get some more feedback on the 
> > > > > current
> > > > > state of the patchseries.
> > > > >
> > > > >
> > > > We are working in memory hotplug functionality on pSeries machine. I'm
> > > > wondering whether and how we can better integrate things. Do you think 
> > > > the
> > > > DIMM abstraction is generic enough to be used in other machine types?
> > > 
> > > I think the DimmDevice is generic enough but I am open to other 
> > > suggestions. 
> > > 
> > > A related issue is that the patchseries uses a DimmBus to hot-add and 
> > > hot-remove
> > > DimmDevice. Another approach that has been suggested is to use links<> 
> > > between
> > > DimmDevices and the dram controller device (piix4 or mch for pc and q35-pc
> > > machines respectively). This would be more similar to the CPUState/qom
> > > patches - see Andreas Färber's earlier reply to this thread.
> > > 
> > > I think we should get some consensus from the community/maintainers 
> > > before we
> > > continue to integrate. 
> > > 
> > > I haven't updated the series for a while, but I can rework if there is a 
> > > more
> > > clear direction for the community.
> > > 
> > > Another open issue is reference counting of memoryregions in qemu memory
> > > model. In order to make memory hot-remove operations safe, we need to 
> > > remove
> > > a memoryregion after all users (e.g. both guest and block layer) have 
> > > stopped
> > > using it,
> > 
> > it seems it mostly up to the user who want to hot-(un)plug,
> > if user want to un-plug a memory which is kernel's main memory, kernel
> > will always run on it(never stop) unless power off.
> > and if guest stops, all DIMMs should be safe to hot-remove,
> > or else we should do something to let user can unlock all reference.
> 
> it's not only the guest-side that needs to stop using it, we need to make sure
> that the qemu block layer is also not using the memory region anymore. See 
> the 2
> links below for discussion:
> 

can't we simply track this(MemoryRegion) usage by ref-count?
e.g.
every time mr used, inc ref-count, then dec it when unused
even for cpu_physical_memory_map and other potential users.

> > >  see discussion at
> > > http://lists.gnu.org/archive/html/qemu-devel/2012-10/msg03986.html. There 
> > > was a
> > > relevant ibm patchset
> > > https://lists.gnu.org/archive/html/qemu-devel/2012-11/msg02697.html
> > > but it was not merged.
> > > 
> thanks,
> 
> - Vasilis