Re: [RFC PATCH 0/10] Another Approach to Use PMEM as NUMA Node

Brice Goglin
2019-03-25T17:45:36Z

Le 25/03/2019 à 17:56, Dan Williams a écrit :
>
> I'm generally against the concept that a "pmem" or "type" flag should
> indicate anything about the expected performance of the address range.
> The kernel should explicitly look to the HMAT for performance data and
> not otherwise make type-based performance assumptions.

Oh sorry, I didn't mean to have the kernel use such a flag to decide of
placement, but rather to expose more information to userspace to clarify
what all these nodes are about when userspace will decide where to
allocate things.

I understand that current NVDIMM-F are not slower than DDR and HMAT
would better describe this than a flag. But I have seen so many buggy or
dummy SLIT tables in the past that I wonder if we can expect HMAT to be
widely available (and correct).

Is there a safe fallback in case of missing or buggy HMAT? For instance,
is DDR supposed to be listed before NVDIMM (or HBM) in SRAT?

Brice