Re: [PATCH][SeaBIOS] memory hotplug

[Gleb Natapov <gleb@redhat.com>]

Commenting a little bit late, but since you've said that you are working on
a new version of the patch... better late than never.

On Thu, Aug 11, 2011 at 04:39:38PM +0200, Vasilis Liaskovitis wrote:
> Hi,
> 
> I am testing a set of experimental patches for memory-hotplug on x86_64 host /
> guest combinations. I have implemented this in a similar way to cpu-hotplug.  
> 
> A dynamic SSDT table with all memory devices is created at boot time.  This
> table calls static methods from the DSDT.  A byte array indicates which memory
> device is online or not. This array is kept in sync with a qemu-kvm bitmap array
> through ioport 0xaf20. Qemu-kvm updates this table on a "mem_set" command and
> an ACPI event is triggered.
> 
> Memory devices are 128MB in size (to match /sys/devices/memory/block_size_bytes 
> in x86_64). They are constructed dynamically in src/ssdt-mem.asl , similarly to
> hotpluggable-CPUs.  The _CRS memstart-memend attribute for each memory device is
> defined accordingly, skipping the hole at 0xe0000000 - 0x100000000.
> Hotpluggable memory is always located above 4GB.
> 
What is the reason for this limitation?

> Qemu-kvm sets the upper bound of hotpluggable memory with "maxmem = [totalmemory in
> MB]" on the command line. Maxmem is an argument for "-m" similar to maxcpus for smp.
> E.g. "-m 1024,maxmem=2048" on the qemu command line will create memory devices
> for 2GB of RAM, enabling only 1GB initially.
> 
> Qemu_monitor triggers a memory hotplug with:
> (qemu) mem_set [memory range in MBs] online
> 
As far as I see mem_set does not get memory range as a parameter. The
parameter is amount of memory to add/remove and memory is added/removed
to/from the top.

This is not flexible enough.  Find grained control for memory slots is
needed. What about exposing memory slot configuration to command line
like this: 

-memslot mem=size,populated=yes|no

adding one of those for each slot.

mem_set will get slot id to populate/depopulate just like cpu_set gets
cpu slot number to remove and not just yanks cpus with highest slot id.

--
			Gleb.