linux-kernel - Re: [PATCH 1/7] node: Link memory nodes to their compute nodes

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Date:   Thu, 15 Nov 2018 07:59:20 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 1/7] node: Link memory nodes to their compute nodes

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?