| Message ID | 1435212855-21685-7-git-send-email-bharata@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Thu, Jun 25, 2015 at 11:44:15AM +0530, Bharata B Rao wrote: > Currently PowerPC kernel doesn't allow hot-adding memory to memory-less > node, but instead will silently add the memory to the first node that has > some memory. This causes two unexpected behaviours for the user. > > Memory gets hotplugged to a different node than what the user specified. > Since pc-dimm subsystem in QEMU still thinks that memory belongs to > memory-less node, a reboot will set things accordingly and the previously > hotplugged memory now ends in the right node. This appears as if some > memory moved from one node to another. > > So until kernel starts supporting memory hotplug to memory-less > nodes, just prevent such attempts upfront in QEMU. > > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com> I presume you're talking about host kernel limitations here? If that does get changed in future we'll need some sort of ugly compat test in qemu to see if the new kernel can handle it, but there's no way to avoid that, so. Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
On Fri, Jun 26, 2015 at 03:33:29PM +1000, David Gibson wrote: > On Thu, Jun 25, 2015 at 11:44:15AM +0530, Bharata B Rao wrote: > > Currently PowerPC kernel doesn't allow hot-adding memory to memory-less > > node, but instead will silently add the memory to the first node that has > > some memory. This causes two unexpected behaviours for the user. > > > > Memory gets hotplugged to a different node than what the user specified. > > Since pc-dimm subsystem in QEMU still thinks that memory belongs to > > memory-less node, a reboot will set things accordingly and the previously > > hotplugged memory now ends in the right node. This appears as if some > > memory moved from one node to another. > > > > So until kernel starts supporting memory hotplug to memory-less > > nodes, just prevent such attempts upfront in QEMU. > > > > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com> > > I presume you're talking about host kernel limitations here? No, this is a guest kernel limitation. Pls refer to the related discussions about this here: https://lkml.org/lkml/2015/6/24/1 > > If that does get changed in future we'll need some sort of ugly compat > test in qemu to see if the new kernel can handle it, but there's no > way to avoid that, so. Yeah, I see that. Regards, Bharata.
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c index f4792b8..003ef14 100644 --- a/hw/ppc/spapr.c +++ b/hw/ppc/spapr.c @@ -2139,6 +2139,28 @@ static void spapr_machine_device_plug(HotplugHandler *hotplug_dev, return; } + /* + * Currently PowerPC kernel doesn't allow hot-adding memory to + * memory-less node, but instead will silently add the memory + * to the first node that has some memory. This causes two + * unexpected behaviours for the user. + * + * - Memory gets hotplugged to a different node than what the user + * specified. + * - Since pc-dimm subsystem in QEMU still thinks that memory belongs + * to memory-less node, a reboot will set things accordingly + * and the previously hotplugged memory now ends in the right node. + * This appears as if some memory moved from one node to another. + * + * So until kernel starts supporting memory hotplug to memory-less + * nodes, just prevent such attempts upfront in QEMU. + */ + if (nb_numa_nodes && !numa_info[node].node_mem) { + error_setg(errp, "Can't hotplug memory to memory-less node %d", + node); + return; + } + spapr_memory_plug(hotplug_dev, dev, node, errp); } }
Currently PowerPC kernel doesn't allow hot-adding memory to memory-less node, but instead will silently add the memory to the first node that has some memory. This causes two unexpected behaviours for the user. Memory gets hotplugged to a different node than what the user specified. Since pc-dimm subsystem in QEMU still thinks that memory belongs to memory-less node, a reboot will set things accordingly and the previously hotplugged memory now ends in the right node. This appears as if some memory moved from one node to another. So until kernel starts supporting memory hotplug to memory-less nodes, just prevent such attempts upfront in QEMU. Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com> --- hw/ppc/spapr.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)