linux-kernel - [PATCH v2 1/3] mm: memory-tiers, numa_emu: enable to create memory tiers using fake numa nodes

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Message-ID: <20251222004834.10539-2-akinobu.mita@gmail.com>
Date: Mon, 22 Dec 2025 09:48:32 +0900
From: Akinobu Mita <akinobu.mita@...il.com>
To: akinobu.mita@...il.com
Cc: linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	akpm@...ux-foundation.org,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	hannes@...xchg.org,
	david@...nel.org,
	mhocko@...nel.org,
	zhengqi.arch@...edance.com,
	shakeel.butt@...ux.dev,
	lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	vbabka@...e.cz,
	rppt@...nel.org,
	surenb@...gle.com
Subject: [PATCH v2 1/3] mm: memory-tiers, numa_emu: enable to create memory tiers using fake numa nodes

This makes it possible to create memory tiers using fake numa nodes
generated by numa emulation.

The "numa_emulation.adistance=" kernel cmdline option allows you to set
the abstract distance for each NUMA node.

For example, you can create two fake nodes, each in a different memory
tier by booting with "numa=fake=2 numa_emulation.adistance=576,704".
Here, the abstract distances of node0 and node1 are set to 576 and 706,
respectively.

Each memory tier covers an abstract distance chunk size of 128. Thus,
nodes with abstract distances between 512 and 639 are classified into the
same memory tier, and nodes with abstract distances between 640 and 767
are classified into the next slower memory tier.

The abstract distance of fake nodes not specified in the parameter will
be the default DRAM abstract distance of 576.

Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
---
v2:
- fix the explanation about cmdline parameter in the commit log

 mm/numa_emulation.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/numa_emulation.c b/mm/numa_emulation.c
index 703c8fa05048..a4266da21344 100644
--- a/mm/numa_emulation.c
+++ b/mm/numa_emulation.c
@@ -6,6 +6,9 @@
 #include <linux/errno.h>
 #include <linux/topology.h>
 #include <linux/memblock.h>
+#include <linux/memory-tiers.h>
+#include <linux/module.h>
+#include <linux/node.h>
 #include <linux/numa_memblks.h>
 #include <asm/numa.h>
 #include <acpi/acpi_numa.h>
@@ -344,6 +347,27 @@ static int __init setup_emu2phys_nid(int *dfl_phys_nid)
 	return max_emu_nid;
 }
 
+static int adistance[MAX_NUMNODES];
+module_param_array(adistance, int, NULL, 0400);
+MODULE_PARM_DESC(adistance, "Abstract distance values for each NUMA node");
+
+static int emu_calculate_adistance(struct notifier_block *self,
+				unsigned long nid, void *data)
+{
+	if (adistance[nid]) {
+		int *adist = data;
+
+		*adist = adistance[nid];
+		return NOTIFY_STOP;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block emu_adist_nb = {
+	.notifier_call = emu_calculate_adistance,
+	.priority = INT_MIN,
+};
+
 /**
  * numa_emulation - Emulate NUMA nodes
  * @numa_meminfo: NUMA configuration to massage
@@ -532,6 +556,8 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 		}
 	}
 
+	register_mt_adistance_algorithm(&emu_adist_nb);
+
 	/* free the copied physical distance table */
 	memblock_free(phys_dist, phys_size);
 	return;
-- 
2.43.0