> >
> > This warning seems to be the following line.
> > ---
> > static int grow_dpa_allocation(struct nd_region *nd_region,
> > struct nd_label_id *label_id, resource_size_t n)
> > {
> > struct nvdimm_bus *nvdimm_bus = walk_to_nvdimm_bus(&nd_region->dev);
> > bool is_pmem = strncmp(label_id->id, "pmem", 4) == 0;
> > int i;
> > :
> > :
> > }
> >
> > dev_WARN_ONCE(&nd_region->dev, rem,
> > <----!!!
> > "allocation underrun: %#llx of %#llx
> > bytes\n", <----!!!
> > (unsigned long long) n - rem,
> > <----!!!
> > (unsigned long long) n);
> > <----!!!
> >
>
> Yes, this appears to be a kernel bug from when
> multiple-namespaces-per-region support was added. The accounting of
> free space that ndctl relies on assumes that all free space is
> contiguous. This assumption was correct in the original
> implementation, but not since commit:
>
> a1f3e4d6a0c3 libnvdimm, region: update nd_region_available_dpa()
> for multi-pmem support
>
> The fix has 3 parts:
>
> 1/ The kernel needs to fail attempts to allocate discontiguous free space
>
> 2/ The kernel needs a new sysfs attribute to export the maximum
> contiguous free space range
>
> 3/ ndctl needs to be updated to pick the max contiguous size rather
> than the max free space
Agree.
Unfortunately, I cound not use the real NVDIMM box which I found this bug now,
because the box is very busy, and the environment will be available
a few months later.
If other person can make the above fixes, it will be faster than me.
Anyone?
>
> Alternatively we could teach the kernel to support discontiguous pmem
> namespaces, but we would need to check if the EFI namespace
> specification allows for such a configuration.
>
I suppose this way is not good way probably.
Though I searched EFI specification 2.7a,
it says just the followings about contiguous namespace,
and I couldn't find any other description.
---
6.1 Block Translation Table (BTT) Background
A namespace defines a contiguously-addressed range of Non-Volatile Memory
conceptually similar to a SCSI Logical Unit (LUN) or a NVM Express
namespace.
---
I also searched "NVDIMM Namespace Specification"
https://pmem.io/documents/NVDIMM_Namespace_Spec.pdf
It say the followings
---
2.6 I/O on Namespaces
A Persistent Memory namespace, by definition, is a contiguous range
of System Physical Address space."
---
So, I could not think that speficications allows discontigous
pmem namespace.
Thanks,
---
Yasunori Goto
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