linux-ext4 - Re: [PATCH v1 00/12] MEMORY_DEVICE_COHERENT for CPU-accessible coherent device memory

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Message-Id: <20211012120322.224d88dad0188160a40dd615@linux-foundation.org>
Date:   Tue, 12 Oct 2021 12:03:22 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Alex Sierra <alex.sierra@....com>, Felix.Kuehling@....com,
        linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jglisse@...hat.com, apopple@...dia.com
Subject: Re: [PATCH v1 00/12] MEMORY_DEVICE_COHERENT for CPU-accessible
 coherent device memory

On Tue, 12 Oct 2021 15:56:29 -0300 Jason Gunthorpe <jgg@...dia.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.