Re: [Qemu-devel] [PATCH] acpi: SRAT: do not create reserved gap entries

[Eduardo Habkost]

On Fri, Aug 10, 2018 at 06:01:06PM +0200, Igor Mammedov wrote:
> On Fri, 10 Aug 2018 16:06:57 +0200
> Igor Mammedov <address@hidden> wrote:
> 
> > Commit 848a1cc1e8b04 while introducing SRAT entries for DIMM and NVDIMM
> > also introduced fake entries for gaps between memory devices, assuming
> > that we need all possible range covered with SRAT entries.
> > And it did it wrong since gap would overlap with preceeding entry.
> > Reproduced with following CLI:
> > 
> >  -m 1G,slots=4,maxmem=8 \
> >  -object memory-backend-ram,size=1G,id=m0 \
> >  -device pc-dimm,memdev=m0,addr=0x101000000 \
> >  -object memory-backend-ram,size=1G,id=m1 \
> >  -device pc-dimm,memdev=m1
> > 
> > However recent development (10efd7e108) showed that gap entries might
> > be not need. And indeed testing with WS2008DC-WS2016DC guests range
> > shows that memory hotplug works just fine without gap entries.
> > 
> > So rather than fixing gap entry borders, just drop them altogether
> > and simplify code around it.
> > 
> > Spotted-by: Laszlo Ersek <address@hidden>
> > Signed-off-by: Igor Mammedov <address@hidden>
> > ---
> > There is no need to update reference blobs since gaps beween dimms
> > aren't generated by any exsting test case.
> > 
> > Considering issue is not visible by default lets just merge it into 3.1
> > and stable 3.0.1
> Pls ignore it for now I'll need to do more extensive testing with old kernels,
> we might need these holes for old kernels or even new ones.
> /me goes to read kernel code
> 
> /per spec possible to hotplug range could be in SRAT,
>  even though I don't like it bu we might end up with static
>  partitioning of hotplug area between nodes like on bare metal
>  to avoid chasing after unknown requirements from windows /

Does that mean we might want to pair DIMM slots with NUMA nodes
in advance?  Do you have a suggestion on how the command-line
would look like, in this case?

Maybe "-numa mem-slot,slot=X,node=Y"?

-- 
Eduardo