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

[Vasilis Liaskovitis]

Hi,

[...]
>> > >
>> > > 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.
>

yes, that's the idea the patchset below try to implement, but last
time I checked this was not upstreamed. I will take a closer look next
week.

>> > >  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.

- Vasilis