selftests/bpf: adapt one more case in test_lru_map to the new target_free

The below commit that updated BPF_MAP_TYPE_LRU_HASH free target,
also updated tools/testing/selftests/bpf/test_lru_map to match.

But that missed one case that passes with 4 cores, but fails at
higher cpu counts.

Update test_lru_sanity3 to also adjust its expectation of target_free.

This time tested with 1, 4, 16, 64 and 384 cpu count.

Fixes: d4adf1c9ee77 ("bpf: Adjust free target to avoid global starvation of LRU map")
Signed-off-by: Willem de Bruijn <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/test_lru_map.c

···
 	return ret;
 }
 
+/* Derive target_free from map_size, same as bpf_common_lru_populate */
+static unsigned int __tgt_size(unsigned int map_size)
+{
+	return (map_size / nr_cpus) / 2;
+}
+
 /* Inverse of how bpf_common_lru_populate derives target_free from map_size. */
 static unsigned int __map_size(unsigned int tgt_free)
 {
···
 	printf("Pass\n");
 }
 
-/* Size of the LRU map is 2*tgt_free
- * It is to test the active/inactive list rotation
- * Insert 1 to 2*tgt_free (+2*tgt_free keys)
- * Lookup key 1 to tgt_free*3/2
- * Add 1+2*tgt_free to tgt_free*5/2 (+tgt_free/2 keys)
- *  => key 1+tgt_free*3/2 to 2*tgt_free are removed from LRU
+/* Test the active/inactive list rotation
+ *
+ * Fill the whole map, deplete the free list.
+ * Reference all except the last lru->target_free elements.
+ * Insert lru->target_free new elements. This triggers one shrink.
+ * Verify that the non-referenced elements are replaced.
  */
 static void test_lru_sanity3(int map_type, int map_flags, unsigned int tgt_free)
 {
···
 
 	assert(sched_next_online(0, &next_cpu) != -1);
 
-	batch_size = tgt_free / 2;
-	assert(batch_size * 2 == tgt_free);
+	batch_size = __tgt_size(tgt_free);
 
 	map_size = tgt_free * 2;
 	lru_map_fd = create_map(map_type, map_flags, map_size);
···
 
 	value[0] = 1234;
 
-	/* Insert 1 to 2*tgt_free (+2*tgt_free keys) */
-	end_key = 1 + (2 * tgt_free);
+	/* Fill the map */
+	end_key = 1 + map_size;
 	for (key = 1; key < end_key; key++)
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
 
-	/* Lookup key 1 to tgt_free*3/2 */
-	end_key = tgt_free + batch_size;
+	/* Reference all but the last batch_size */
+	end_key = 1 + map_size - batch_size;
 	for (key = 1; key < end_key; key++) {
 		assert(!bpf_map_lookup_elem_with_ref_bit(lru_map_fd, key, value));
 		assert(!bpf_map_update_elem(expected_map_fd, &key, value,
 					    BPF_NOEXIST));
 	}
 
-	/* Add 1+2*tgt_free to tgt_free*5/2
-	 * (+tgt_free/2 keys)
-	 */
+	/* Insert new batch_size: replaces the non-referenced elements */
 	key = 2 * tgt_free + 1;
 	end_key = key + batch_size;
 	for (; key < end_key; key++) {