linux-kernel - Re: [RFC] cxl/region: set numa node for target memdevs when a region is committed

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Message-ID: <67d9e4d43360e_201f0294d6@dwillia2-xfh.jf.intel.com.notmuch>
Date: Tue, 18 Mar 2025 14:25:40 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Dave Jiang <dave.jiang@...el.com>, <nifan.cxl@...il.com>,
	<alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
	<ira.weiny@...el.com>, <dan.j.williams@...el.com>,
	<Jonathan.Cameron@...wei.com>
CC: <linux-cxl@...r.kernel.org>, <a.manzanares@...sung.com>,
	<dave@...olabs.net>, <linux-kernel@...r.kernel.org>, <anisa.su887@...il.com>,
	Fan Ni <fan.ni@...sung.com>
Subject: Re: [RFC] cxl/region: set numa node for target memdevs when a region
 is committed

Dave Jiang wrote:
> 
> 
> On 3/14/25 9:40 AM, nifan.cxl@...il.com wrote:
> > From: Fan Ni <fan.ni@...sung.com>
> > 
> > There is a sysfs attribute named "numa_node" for cxl memory device.
> > however, it is never set so -1 is returned whenever it is read.
> > 
> > With this change, the numa_node of each target memdev is set based on the
> > start address of the hpa_range of the endpoint decoder it associated when a
> > cxl region is created; and it is reset when the region decoders are
> > reset.
> > 
> > Open qeustion: do we need to set the numa_node when the memdev is
> > probed instead of waiting until a region is created?
> 
> Typically, the numa node for a PCI device should be dev_to_node(),
> where the device resides. So when the device is probed, it should be
> set with that. See documentation [1]. Region should have its own NUMA
> node based on phys_to_target_node() of the starting address.  

Right, the memdev node is the affinity of device-MMIO to a CPU. The
HDM-memory that the device decodes may land in multiple proximity
domains and is subject to CDAT, CXL QoS, HMAT Generic Port, etc...

If your memdev node is "NUMA_NO_NODE" then that likely means the
affinity information for the PCI device is missing.

I would double check that first. See set_dev_node() in device_add().