selftest/vm: fix ksm selftest to run with different NUMA topologies

Platforms can have non-contiguous NUMA nodes like below

   #numactl  -H
  available: 2 nodes (0,8)
  .....
  node distances:
  node   0   8
    0:  10  40
    8:  40  10

   #numactl  -H
  available: 1 nodes (1)
  ....
  node distances:
  node   1
    1:  10

Hence update the test to not assume the presence of Node 0 and 1 and
also use numa_num_configured_nodes() instead of numa_max_node for
finding whether to skip the test.

Link: https://lkml.kernel.org/r/20210914141414.350759-1-aneesh.kumar@linux.ibm.com
Fixes: 82e717ad35 ("selftests: vm: add KSM merging across nodes test")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Zhansaya Bagdauletkyzy <zhansayabagdaulet@gmail.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/ksm_tests.c

@@ -354,12 +354,34 @@ err_out:
 	return KSFT_FAIL;
 }
 
+static int get_next_mem_node(int node)
+{
+
+	long node_size;
+	int mem_node = 0;
+	int i, max_node = numa_max_node();
+
+	for (i = node + 1; i <= max_node + node; i++) {
+		mem_node = i % (max_node + 1);
+		node_size = numa_node_size(mem_node, NULL);
+		if (node_size > 0)
+			break;
+	}
+	return mem_node;
+}
+
+static int get_first_mem_node(void)
+{
+	return get_next_mem_node(numa_max_node());
+}
+
 static int check_ksm_numa_merge(int mapping, int prot, int timeout, bool merge_across_nodes,
 				size_t page_size)
 {
 	void *numa1_map_ptr, *numa2_map_ptr;
 	struct timespec start_time;
 	int page_count = 2;
+	int first_node;
 
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
 		perror("clock_gettime");
@@ -370,7 +392,7 @@ static int check_ksm_numa_merge(int mapping, int prot, int timeout, bool merge_a
 		perror("NUMA support not enabled");
 		return KSFT_SKIP;
 	}
-	if (numa_max_node() < 1) {
+	if (numa_num_configured_nodes() <= 1) {
 		printf("At least 2 NUMA nodes must be available\n");
 		return KSFT_SKIP;
 	}
@@ -378,8 +400,9 @@ static int check_ksm_numa_merge(int mapping, int prot, int timeout, bool merge_a
 		return KSFT_FAIL;
 
 	/* allocate 2 pages in 2 different NUMA nodes and fill them with the same data */
-	numa1_map_ptr = numa_alloc_onnode(page_size, 0);
-	numa2_map_ptr = numa_alloc_onnode(page_size, 1);
+	first_node = get_first_mem_node();
+	numa1_map_ptr = numa_alloc_onnode(page_size, first_node);
+	numa2_map_ptr = numa_alloc_onnode(page_size, get_next_mem_node(first_node));
 	if (!numa1_map_ptr || !numa2_map_ptr) {
 		perror("numa_alloc_onnode");
 		return KSFT_FAIL;