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Date: Mon, 19 Nov 2018 08:22:49 +0530 From: Anshuman Khandual <anshuman.khandual@....com> To: Keith Busch <keith.busch@...el.com>, 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 11/15/2018 08:29 PM, Keith Busch 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? Having hint for local affinity is definitely a plus but this must provide the coherency matrix to the user preferably in the form of a nodemask for each memory target.
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