Re: [RFC PATCH 0/9] ACPI memory hotplug

[Gleb Natapov <gleb@redhat.com>]

On Tue, Apr 24, 2012 at 10:24:51AM +0200, Vasilis Liaskovitis wrote:
> Hi,
> On Tue, Apr 24, 2012 at 10:52:24AM +0300, Gleb Natapov wrote:
> > On Mon, Apr 23, 2012 at 02:31:15PM +0200, Vasilis Liaskovitis wrote:
> > > The 440fx spec mentions: "The address range from the top of main DRAM to 4
> > > Gbytes (top of physical memory space supported by the 440FX PCIset) is normally
> > > mapped to PCI. The PMC forwards all accesses within this address range to PCI."
> > > 
> > > What we probably want is that the initial memory map creation takes into account
> > > all dimms specified (both populated/unpopulated) 
> > Yes.
> > 
> > > So "-m 1G, -device dimm,size=1G,populated=true -device dimm,size=1G,populated=false"
> > > would create a system map with top of memory and start of PCI-hole at 2G. 
> > > 
> > What -m 1G means on this command line? Isn't it redundant?
> yes, this was redundant with the original concept.
> 
> > May be we should make -m create non unplaggable, populated slot starting
> > at address 0. Ten you config above will specify 3G memory with 2G
> > populated (first of which is not removable) and 1G unpopulated. PCI hole
> > starts above 3G.
> 
> I agree -m should mean one big unpluggable slot.
> 
> So in the new proposal,"-device dimm populated=true" means a hot-removable dimm
> that has already been hotplugged. 
> 
Yes.

> A question here is when exactly should the initial hot-add event for this dimm
> be played? If the relevant OSPM has not yet been initialized (e.g. acpi_memhotplug
> module in a linux guest needs to be loaded), the guest may not see the event. 
> This is a general issue of course, but with initially populated hot-removable
> dimms it may be a bigger issue. Can ospm acpi initialization be detected?
> 
> Or maybe you are suggesting "populated=true" is part of initial memory (i.e. not
> hot-added, but still hot-removable). Though in that case guestOS may use it for
> bootmem allocations, making hot-remove more likely to fail at the memory
> offlining stage.
>
If memory slot is populated even before OSPM is started BIOS will detect
that by reading mem_sts and will create e820 map appropriately. OSPM
will detect it by evaluating _STA during boot. This is not unique for
memory hot-plug. Any hotpluggable device have the same issue.

--
			Gleb.