[PATCH 2/2] selftests/mm: fix ksm NUMA merge test for systems with memoryless NUMA nodes

The KSM NUMA merge test allocates identical pages on different NUMA
nodes and verifies KSM behavior with merge_across_nodes enabled and
disabled.

On systems with memoryless NUMA nodes, for example:
 #numactl  -H
      available: 2 nodes (0,4)
      .....
      node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
      node 0 size: 14825 MB
      node 0 free: 1382 MB
      node 4 cpus:
      node 4 size: 0 MB
      node 4 free: 0 MB

the test may attempt to allocate memory on a node without memory,
causing numa_alloc_onnode() to fail and resulting in a spurious test
failure.

Add count_mem_nodes() helper to count only nodes with memory and use it
instead of numa_num_configured_nodes() to ensure the test runs only on
systems with at least two NUMA nodes that have memory. Skip the test
otherwise.

Before patch:
       ---------------------------
	running ./ksm_tests -N -m 1
       ---------------------------
        mbind: Invalid argument
        ok 1 KSM NUMA merging
	Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
        [PASS]
       ok 1 ksm_tests -N -m 1
       ---------------------------
        running ./ksm_tests -N -m 0
       ---------------------------
        mbind: Invalid argument
        not ok 1 KSM NUMA merging
	Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0
        [FAIL]
       not ok 2 ksm_tests -N -m 0 # exit=1

After patch:
       ---------------------------
        running ./ksm_tests -N -m 1
       ---------------------------
        SKIP At least 2 NUMA nodes with memory must be available
	Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
        [SKIP]
        ok 1 ksm_tests -N -m 1 # SKIP
       ---------------------------
        running ./ksm_tests -N -m 0
       ---------------------------
        SKIP At least 2 NUMA nodes with memory must be available
	Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
        [SKIP]
        ok 2 ksm_tests -N -m 0 # SKIP

Fixes: e3820ab252dd ("selftest/vm: fix ksm selftest to run with different NUMA topologies")
Signed-off-by: Sayali Patil <redacted>
---
 tools/testing/selftests/mm/ksm_tests.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index a050f4840cfa..d1790b4347d3 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c

@@ -450,6 +450,18 @@ static int get_first_mem_node(void)
 	return get_next_mem_node(numa_max_node());
 }
 
+static int count_mem_nodes(void)
+{
+	int node, count = 0;
+
+	for (node = 0; node <= numa_max_node(); node++) {
+		if (numa_node_size(node, NULL) > 0)
+			count++;
+	}
+
+	return count;
+}
+
 static int check_ksm_numa_merge(int merge_type, int mapping, int prot, int timeout,
 				bool merge_across_nodes, size_t page_size)
 {

@@ -463,14 +475,12 @@ static int check_ksm_numa_merge(int merge_type, int mapping, int prot, int timeo
 		return KSFT_FAIL;
 	}
 
-	if (numa_available() < 0) {
-		ksft_print_msg("NUMA support not enabled\n");
-		return KSFT_SKIP;
-	}
-	if (numa_num_configured_nodes() <= 1) {
-		ksft_print_msg("At least 2 NUMA nodes must be available\n");
-		return KSFT_SKIP;
-	}
+	if (numa_available() < 0)
+		ksft_exit_skip("NUMA support not enabled\n");
+
+	if (count_mem_nodes() <= 1)
+		ksft_exit_skip("At least 2 NUMA nodes with memory must be available\n");
+
 	if (ksm_write_sysfs(KSM_FP("merge_across_nodes"), merge_across_nodes))
 		return KSFT_FAIL;
 

-- 
2.52.0