lib: add a function to lock memory into RAM

Add a function to lock memory into RAM and use it in the
gem_tiled_swapping test to reduce the amount of allocated memory
required to force swapping. This also reduces the amount of time
required for the test to complete, since the data set is smaller.

The following durations were recorded with gem_tiled_swapping on a
haswell system before the change:

  Subtest non-threaded: SUCCESS (55.889s)
  Subtest threaded: SUCCESS (810.532s)

and after:

  Subtest non-threaded: SUCCESS (11.804s)
  Subtest threaded: SUCCESS (268.336s)

v2: add various assertions and requirements and make sure
    gem_tiled_swapping works on systems with less RAM (Daniel Vetter)

v3: fix allocation size calculation

Signed-off-by: Thomas Wood <thomas.wood@intel.com>

2 files changed, 61 insertions, 0 deletions

diff --git a/lib/igt_aux.c b/lib/igt_aux.c
index 3051d84c..11618282 100644
--- a/lib/igt_aux.c
+++ b/lib/igt_aux.c
@@ -601,3 +601,61 @@ struct type_name connector_type_names[] = {
 };
 
 type_name_fn(connector_type)
+
+
+/**
+ * igt_lock_mem:
+ * @size: the amount of memory to lock into RAM, in MB
+ *
+ * Allocate @size MB of memory and lock it into RAM. This releases any
+ * previously locked memory.
+ *
+ * Use #igt_unlock_mem to release the currently locked memory.
+ */
+static char *locked_mem;
+static size_t locked_size;
+
+void igt_lock_mem(size_t size)
+{
+	long pagesize = sysconf(_SC_PAGESIZE);
+	size_t i;
+	int ret;
+
+	if (size == 0) {
+		return;
+	}
+
+	if (locked_mem) {
+		igt_unlock_mem();
+		igt_warn("Unlocking previously locked memory.\n");
+	}
+
+	locked_size = size * 1024 * 1024;
+
+	locked_mem = malloc(locked_size);
+	igt_require_f(locked_mem,
+		      "Could not allocate enough memory to lock.\n");
+
+	/* write into each page to ensure it is allocated */
+	for (i = 0; i < locked_size; i += pagesize)
+		locked_mem[i] = i;
+
+	ret = mlock(locked_mem, locked_size);
+	igt_assert_f(ret == 0, "Could not lock memory into RAM.\n");
+}
+
+/**
+ * igt_unlock_mem:
+ *
+ * Release and free the RAM used by #igt_lock_mem.
+ */
+void igt_unlock_mem(void)
+{
+	if (!locked_mem)
+		return;
+
+	munlock(locked_mem, locked_size);
+
+	free(locked_mem);
+	locked_mem = NULL;
+}
diff --git a/lib/igt_aux.h b/lib/igt_aux.h
index 63e1b06a..c420b3ff 100644
--- a/lib/igt_aux.h
+++ b/lib/igt_aux.h
@@ -96,4 +96,7 @@ void intel_require_memory(uint32_t count, uint32_t size, unsigned mode);
 	(b) = _tmp;		\
 } while (0)
 
+void igt_lock_mem(size_t size);
+void igt_unlock_mem(void);
+
 #endif /* IGT_AUX_H */