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References: <20181114224921.12123-2-keith.busch@intel.com> <20181115135710.GD19286@bombadil.infradead.org>
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From: Dan Williams <dan.j.williams@intel.com>
Date: Thu, 15 Nov 2018 09:50:58 -0800
Message-ID: <CAPcyv4iLSiJz6Z7qyjqpo=HUZQy-gAcaG69JytLPPGqOO157sg@mail.gmail.com>
Subject: Re: [PATCH 1/7] node: Link memory nodes to their compute nodes
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Sender: owner-linux-mm@kvack.org
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To: Keith Busch <keith.busch@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Linux ACPI <linux-acpi@vger.kernel.org>, Linux MM <linux-mm@kvack.org>, Greg KH <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, Dave Hansen <dave.hansen@intel.com>

On Thu, Nov 15, 2018 at 7:02 AM Keith Busch <keith.busch@intel.com> wrote:
>
> On Thu, Nov 15, 2018 at 05:57:10AM -0800, Matthew Wilcox wrote:
> > On Wed, Nov 14, 2018 at 03:49:14PM -0700, Keith Busch wrote:
> > > Memory-only nodes will often have affinity to a compute node, and
> > > platforms have ways to express that locality relationship.
> > >
> > > A node containing CPUs or other DMA devices that can initiate memory
> > > access are referred to as "memory iniators". A "memory target" is a
> > > node that provides at least one phyiscal address range accessible to a
> > > memory initiator.
> >
> > I think I may be confused here.  If there is _no_ link from node X to
> > node Y, does that mean that node X's CPUs cannot access the memory on
> > node Y?  In my mind, all nodes can access all memory in the system,
> > just not with uniform bandwidth/latency.
>
> The link is just about which nodes are "local". It's like how nodes have
> a cpulist. Other CPUs not in the node's list can acces that node's memory,
> but the ones in the mask are local, and provide useful optimization hints.
>
> Would a node mask would be prefered to symlinks?

I think that would be more flexible, because the set of initiators
that may have "best" or "local" access to a target may be more than 1.