Mel,
As of commit 8a942fdea560d4ac0e9d9fabcd5201ad20e0c382 (mm: meminit: make
__early_pfn_to_nid SMP-safe and introduce meminit_pfn_in_nid)
vmemmap_verify() will BUG_ON() during memory hotplug because of its use
of early_pfn_to_nid(). Previously, it would have reported bogus (or
failed to report valid) warnings.
I believe this does not affect memory hotplug on most x86 systems
because vmemmap_populate() would normally call
vmemmap_populate_hugepages() which avoids calling vmemmap_verify() in
the common case (no existing mappings covering the new area).
I'm triggering the early_pfn_to_nid() BUG_ON() with the Xen balloon
driver in a PV guest which will always call vmemmap_populate_basepages()
(since Xen PV guests lack superpage support).
Not really sure what the best way to resolve this is. Presumably
vmmemmap_verify() needs to switch to using pfn_to_nid() after the
initial initialization but there doesn't appear to be anything suitable
to distinguish between the early and hotplug cases.
David
On Mon, Jul 27, 2015 at 04:32:45PM +0100, David Vrabel wrote:
> Mel,
>
> As of commit 8a942fdea560d4ac0e9d9fabcd5201ad20e0c382 (mm: meminit: make
> __early_pfn_to_nid SMP-safe and introduce meminit_pfn_in_nid)
> vmemmap_verify() will BUG_ON() during memory hotplug because of its use
> of early_pfn_to_nid(). Previously, it would have reported bogus (or
> failed to report valid) warnings.
>
Please test "mm, meminit: Allow early_pfn_to_nid to be used during
runtime"
--
Mel Gorman
SUSE Labs
On 27/07/15 16:41, Mel Gorman wrote:
> On Mon, Jul 27, 2015 at 04:32:45PM +0100, David Vrabel wrote:
>> Mel,
>>
>> As of commit 8a942fdea560d4ac0e9d9fabcd5201ad20e0c382 (mm: meminit: make
>> __early_pfn_to_nid SMP-safe and introduce meminit_pfn_in_nid)
>> vmemmap_verify() will BUG_ON() during memory hotplug because of its use
>> of early_pfn_to_nid(). Previously, it would have reported bogus (or
>> failed to report valid) warnings.
>>
>
> Please test "mm, meminit: Allow early_pfn_to_nid to be used during
> runtime"
That fixed the BUG_ON() thanks. But I still can't only the new sections
because their first page is not reserved, but I've not had time to
investigate why this is yet.
David