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

The new "numa_emulation.adistance" kernel parameter allows you to set the
abstract distance for each NUMA node.

For example, if the system is booted with the parameters
"numa=fake=2 numa_emulation.adistance=576,704", it will configure memory
tiers with node0 having the default DRAM adistance value and node1 having
a lower adistance value.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 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