mm/fake-numa: allow later numa node hotplug

Current fake-numa implementation prevents new Numa nodes to be later
hot-plugged by drivers.  A common symptom of this limitation is the "node
<X> was absent from the node_possible_map" message by associated warning
in mm/memory_hotplug.c: add_memory_resource().

This comes from the lack of remapping in both pxm_to_node_map[] and
node_to_pxm_map[] tables to take fake-numa nodes into account and thus
triggers collisions with original and physical nodes only-mapping that had
been determined from BIOS tables.

This patch fixes this by doing the necessary node-ids translation in both
pxm_to_node_map[]/node_to_pxm_map[] tables.  node_distance[] table has
also been fixed accordingly.


Details:

When trying to use fake-numa feature on our system where new Numa nodes
are being "hot-plugged" upon driver load, this fails with the following
type of message and warning with stack :

node 8 was absent from the node_possible_map WARNING: CPU: 61 PID: 4259 at
mm/memory_hotplug.c:1506 add_memory_resource+0x3dc/0x418

This issue prevents the use of the fake-NUMA debug feature with the
system's full configuration, when it has proven to be sometimes extremely
useful for performance testing of multi-tasked, memory-bound applications,
as it enables better isolation of processes/ranks compared to fat NUMA
nodes.

Usual numactl output after driver has “hot-plugged”/unveiled some
new Numa nodes with and without memory :
$ numactl --hardware
available: 9 nodes (0-8)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 0 size: 490037 MB
node 0 free: 484432 MB
node 1 cpus:
node 1 size: 97280 MB
node 1 free: 97279 MB
node 2 cpus:
node 2 size: 0 MB
node 2 free: 0 MB
node 3 cpus:
node 3 size: 0 MB
node 3 free: 0 MB
node 4 cpus:
node 4 size: 0 MB
node 4 free: 0 MB
node 5 cpus:
node 5 size: 0 MB
node 5 free: 0 MB
node 6 cpus:
node 6 size: 0 MB
node 6 free: 0 MB
node 7 cpus:
node 7 size: 0 MB
node 7 free: 0 MB
node 8 cpus:
node 8 size: 0 MB
node 8 free: 0 MB
node distances:
node   0   1   2   3   4   5   6   7   8
  0:  10  80  80  80  80  80  80  80  80
  1:  80  10  255  255  255  255  255  255  255
  2:  80  255  10  255  255  255  255  255  255
  3:  80  255  255  10  255  255  255  255  255
  4:  80  255  255  255  10  255  255  255  255
  5:  80  255  255  255  255  10  255  255  255
  6:  80  255  255  255  255  255  10  255  255
  7:  80  255  255  255  255  255  255  10  255
  8:  80  255  255  255  255  255  255  255  10


With recent M.Rapoport set of fake-numa patches in mm-everything
and using numa=fake=4 boot parameter :
$ numactl --hardware
available: 4 nodes (0-3)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 0 size: 122518 MB
node 0 free: 117141 MB
node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 1 size: 219911 MB
node 1 free: 219751 MB
node 2 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 2 size: 122599 MB
node 2 free: 122541 MB
node 3 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 3 size: 122479 MB
node 3 free: 122408 MB
node distances:
node   0   1   2   3
  0:  10  10  10  10
  1:  10  10  10  10
  2:  10  10  10  10
  3:  10  10  10  10


With recent M.Rapoport set of fake-numa patches in mm-everything,
this patch on top, using numa=fake=4 boot parameter :
# numactl —hardware
available: 12 nodes (0-11)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 0 size: 122518 MB
node 0 free: 116429 MB
node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 1 size: 122631 MB
node 1 free: 122576 MB
node 2 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 2 size: 122599 MB
node 2 free: 122544 MB
node 3 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
65 66 67 68 69 70 71
node 3 size: 122479 MB
node 3 free: 122419 MB
node 4 cpus:
node 4 size: 97280 MB
node 4 free: 97279 MB
node 5 cpus:
node 5 size: 0 MB
node 5 free: 0 MB
node 6 cpus:
node 6 size: 0 MB
node 6 free: 0 MB
node 7 cpus:
node 7 size: 0 MB
node 7 free: 0 MB
node 8 cpus:
node 8 size: 0 MB
node 8 free: 0 MB
node 9 cpus:
node 9 size: 0 MB
node 9 free: 0 MB
node 10 cpus:
node 10 size: 0 MB
node 10 free: 0 MB
node 11 cpus:
node 11 size: 0 MB
node 11 free: 0 MB
node distances:
node   0   1   2   3   4   5   6   7   8   9  10  11
  0:  10  10  10  10  80  80  80  80  80  80  80  80
  1:  10  10  10  10  80  80  80  80  80  80  80  80
  2:  10  10  10  10  80  80  80  80  80  80  80  80
  3:  10  10  10  10  80  80  80  80  80  80  80  80
  4:  80  80  80  80  10  255  255  255  255  255  255  255
  5:  80  80  80  80  255  10  255  255  255  255  255  255
  6:  80  80  80  80  255  255  10  255  255  255  255  255
  7:  80  80  80  80  255  255  255  10  255  255  255  255
  8:  80  80  80  80  255  255  255  255  10  255  255  255
  9:  80  80  80  80  255  255  255  255  255  10  255  255
 10:  80  80  80  80  255  255  255  255  255  255  10  255
 11:  80  80  80  80  255  255  255  255  255  255  255  10

Link: https://lkml.kernel.org/r/20250106120659.359610-2-bfaccini@nvidia.com
Signed-off-by: Bruno Faccini <bfaccini@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 39 insertions, 8 deletions

diff --git a/mm/numa_emulation.c b/mm/numa_emulation.c
index 031fb9961bf7..9d55679d99ce 100644
--- a/mm/numa_emulation.c
+++ b/mm/numa_emulation.c
@@ -8,11 +8,12 @@
 #include <linux/memblock.h>
 #include <linux/numa_memblks.h>
 #include <asm/numa.h>
+#include <acpi/acpi_numa.h>
 
 #define FAKE_NODE_MIN_SIZE	((u64)32 << 20)
 #define FAKE_NODE_MIN_HASH_MASK	(~(FAKE_NODE_MIN_SIZE - 1UL))
 
-static int emu_nid_to_phys[MAX_NUMNODES];
+int emu_nid_to_phys[MAX_NUMNODES];
 static char *emu_cmdline __initdata;
 
 int __init numa_emu_cmdline(char *str)
@@ -379,6 +380,7 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 	size_t phys_size = numa_dist_cnt * numa_dist_cnt * sizeof(phys_dist[0]);
 	int max_emu_nid, dfl_phys_nid;
 	int i, j, ret;
+	nodemask_t physnode_mask = numa_nodes_parsed;
 
 	if (!emu_cmdline)
 		goto no_emu;
@@ -395,7 +397,6 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 	 * split the system RAM into N fake nodes.
 	 */
 	if (strchr(emu_cmdline, 'U')) {
-		nodemask_t physnode_mask = numa_nodes_parsed;
 		unsigned long n;
 		int nid = 0;
 
@@ -465,9 +466,6 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 	 */
 	max_emu_nid = setup_emu2phys_nid(&dfl_phys_nid);
 
-	/* commit */
-	*numa_meminfo = ei;
-
 	/* Make sure numa_nodes_parsed only contains emulated nodes */
 	nodes_clear(numa_nodes_parsed);
 	for (i = 0; i < ARRAY_SIZE(ei.blk); i++)
@@ -475,10 +473,21 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 		    ei.blk[i].nid != NUMA_NO_NODE)
 			node_set(ei.blk[i].nid, numa_nodes_parsed);
 
-	numa_emu_update_cpu_to_node(emu_nid_to_phys, ARRAY_SIZE(emu_nid_to_phys));
+	/* fix pxm_to_node_map[] and node_to_pxm_map[] to avoid collision
+	 * with faked numa nodes, particularly during later memory hotplug
+	 * handling, and also update numa_nodes_parsed accordingly.
+	 */
+	ret = fix_pxm_node_maps(max_emu_nid);
+	if (ret < 0)
+		goto no_emu;
+
+	/* commit */
+	*numa_meminfo = ei;
+
+	numa_emu_update_cpu_to_node(emu_nid_to_phys, max_emu_nid + 1);
 
 	/* make sure all emulated nodes are mapped to a physical node */
-	for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++)
+	for (i = 0; i < max_emu_nid + 1; i++)
 		if (emu_nid_to_phys[i] == NUMA_NO_NODE)
 			emu_nid_to_phys[i] = dfl_phys_nid;
 
@@ -501,12 +510,34 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 			numa_set_distance(i, j, dist);
 		}
 	}
+	for (i = 0; i < numa_distance_cnt; i++) {
+		for (j = 0; j < numa_distance_cnt; j++) {
+			int physi, physj;
+			u8 dist;
+
+			/* distance between fake nodes is already ok */
+			if (emu_nid_to_phys[i] != NUMA_NO_NODE &&
+			    emu_nid_to_phys[j] != NUMA_NO_NODE)
+				continue;
+			if (emu_nid_to_phys[i] != NUMA_NO_NODE)
+				physi = emu_nid_to_phys[i];
+			else
+				physi = i - max_emu_nid;
+			if (emu_nid_to_phys[j] != NUMA_NO_NODE)
+				physj = emu_nid_to_phys[j];
+			else
+				physj = j - max_emu_nid;
+			dist = phys_dist[physi * numa_dist_cnt + physj];
+			numa_set_distance(i, j, dist);
+		}
+	}
 
 	/* free the copied physical distance table */
 	memblock_free(phys_dist, phys_size);
 	return;
 
 no_emu:
+	numa_nodes_parsed = physnode_mask;
 	/* No emulation.  Build identity emu_nid_to_phys[] for numa_add_cpu() */
 	for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++)
 		emu_nid_to_phys[i] = i;
diff --git a/mm/numa_memblks.c b/mm/numa_memblks.c
index a3877e9bc878..ff4054f4334d 100644
--- a/mm/numa_memblks.c
+++ b/mm/numa_memblks.c
@@ -7,7 +7,7 @@
 #include <linux/numa.h>
 #include <linux/numa_memblks.h>
 
-static int numa_distance_cnt;
+int numa_distance_cnt;
 static u8 *numa_distance;
 
 nodemask_t numa_nodes_parsed __initdata;