Re: [PATCH v1 00/12] MEMORY_DEVICE_COHERENT for CPU-accessible coherent device memory

Andrew Morton
2021-10-12T19:05:14Z

On Tue, 12 Oct 2021 15:56:29 -0300 Jason Gunthorpe <jgg@nvidia.com> wrote:

> > To what other uses will this infrastructure be put?
> >
> > Because I must ask: if this feature is for one single computer which
> > presumably has a custom kernel, why add it to mainline Linux?
>
> Well, it certainly isn't just "one single computer". Overall I know of
> about, hmm, ~10 *datacenters* worth of installations that are using
> similar technology underpinnings.
>
> "Frontier" is the code name for a specific installation but as the
> technology is proven out there will be many copies made of that same
> approach.
>
> The previous program "Summit" was done with NVIDIA GPUs and PowerPC
> CPUs and also included a very similar capability. I think this is a
> good sign that this coherently attached accelerator will continue to
> be a theme in computing going foward. IIRC this was done using out of
> tree kernel patches and NUMA localities.
>
> Specifically with CXL now being standardized and on a path to ubiquity
> I think we will see an explosion in deployments of coherently attached
> accelerator memory. This is the high end trickling down to wider
> usage.
>
> I strongly think many CXL accelerators are going to want to manage
> their on-accelerator memory in this way as it makes universal sense to
> want to carefully manage memory access locality to optimize for
> performance.

Thanks. Can we please get something like the above into the [0/n]
changelog? Along with any other high-level info which is relevant?

It's rather important. "why should I review this", "why should we
merge this", etc.