From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-f200.google.com (mail-oi1-f200.google.com [209.85.167.200]) by kanga.kvack.org (Postfix) with ESMTP id 7E5346B181E for ; Sun, 18 Nov 2018 21:52:55 -0500 (EST) Received: by mail-oi1-f200.google.com with SMTP id r3-v6so16212758oif.7 for ; Sun, 18 Nov 2018 18:52:55 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id y8si21307707otb.143.2018.11.18.18.52.53 for ; Sun, 18 Nov 2018 18:52:53 -0800 (PST) Subject: Re: [PATCH 1/7] node: Link memory nodes to their compute nodes References: <20181114224921.12123-2-keith.busch@intel.com> <20181115135710.GD19286@bombadil.infradead.org> <20181115145920.GG11416@localhost.localdomain> From: Anshuman Khandual Message-ID: Date: Mon, 19 Nov 2018 08:22:49 +0530 MIME-Version: 1.0 In-Reply-To: <20181115145920.GG11416@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Keith Busch , Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-mm@kvack.org, Greg Kroah-Hartman , Rafael Wysocki , Dave Hansen , Dan Williams 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.