[PATCH v2 2/2] lib/igt_core.c: add function to disable lowmemorykiller

[tim.gore@intel.com]

From: Tim Gore <tim.gore@intel.com>

Several IGT tests put a lot of pressure on memory and
when running these tests on Android they tend to get
killed by the lowmemorykiller. The lowmemorykiller really
is not usefull in this context and is just preventing the
test from doing its job. This commit adds a function to
disable the lowmemorykiller by writing "9999" to its
oom adj parameter, which means it will never "select"
any process to kill. The normal linux oom killer is still
there to protect the kernel.
This function is not called by default; it is up to each
individual test to call this function if it might trigger
the lowmemorykiller.
The igt_exit() now includes a call to this function to
re-enable the lowmemorykiller if it has been disabled.
A test may also re-enable the lowmemorykiller once it is
finished since this is benign if called more than once.

Signed-off-by: Tim Gore <tim.gore@intel.com>
---
 lib/igt_core.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/lib/igt_core.c b/lib/igt_core.c
index 9344815..172a204 100644
--- a/lib/igt_core.c
+++ b/lib/igt_core.c
@@ -326,6 +326,72 @@ static void print_usage(const char *help_str, bool output_on_stderr)
 		fprintf(f, "%s\n", help_str);
 }
 
+
+/* Some of the IGT tests put quite a lot of pressure on memory and when
+ * running on Android they are sometimes killed by the Android low memory killer.
+ * The low memory killer really isn't usefull in this context and has no
+ * interaction with the gpu driver that we are testing, so the following
+ * function is used to disable it by modifying one of its module parameters.
+ * We still have the normal linux oom killer to protect the kernel.
+ * Apparently it is also possible for the lowmemorykiller to get included
+ * in some linux distributions; so rather than check for Android we directly
+ * check for the existence of the module parameter we want to adjust.
+ */
+void low_mem_killer_disable(bool disable)
+{
+	static const char* adj_fname="/sys/module/lowmemorykiller/parameters/adj";
+	static const char no_lowmem_killer[] = "9999";
+	int fd;
+	struct stat buf;
+	/* The following must persist across invocations */
+	static char prev_adj_scores[256];
+	static int adj_scores_len = 0;
+	static bool is_disabled = false;
+
+	/* check to see if there is something to do */
+	if (!(disable ^ is_disabled))
+		return;
+
+	/* capture the permissions bits for the lowmemkiller adj pseudo-file.
+	   Bail out if the stat fails; it probably means that there is no
+	   lowmemorykiller, but in any case we're doomed. */
+	if (stat (adj_fname, &buf))
+	{
+		igt_assert(errno == ENOENT);
+		return;
+	}
+	/* make sure the file can be read/written - by default it is write-only */
+	chmod (adj_fname, S_IRUSR | S_IWUSR);
+
+	if (disable)
+	{
+		/* read the current oom adj parameters for lowmemorykiller */
+		fd = open(adj_fname, O_RDWR);
+		igt_assert(fd != -1);
+		adj_scores_len = read(fd, (void*)prev_adj_scores, 255);
+		igt_assert(adj_scores_len > 0);
+
+		/* writing 9999 to this module parameter effectively diables the
+		 * low memory killer. This is not a real file, so we dont need to
+		 * seek to the start or truncate it */
+		write(fd, no_lowmem_killer, sizeof(no_lowmem_killer));
+		close(fd);
+		is_disabled = true;
+	}
+	else
+	{
+		/* just re-enstate the original settings */
+		fd = open(adj_fname, O_WRONLY);
+		igt_assert(fd != -1);
+		write(fd, prev_adj_scores, adj_scores_len);
+		close(fd);
+		is_disabled = false;
+	}
+
+	/* re-enstate the file permissions */
+	chmod (adj_fname, buf.st_mode);
+}
+
 static void oom_adjust_for_doom(void)
 {
 	int fd;
@@ -334,6 +400,7 @@ static void oom_adjust_for_doom(void)
 	fd = open("/proc/self/oom_score_adj", O_WRONLY);
 	igt_assert(fd != -1);
 	igt_assert(write(fd, always_kill, sizeof(always_kill)) == sizeof(always_kill));
+	close(fd);
 }
 
 static int common_init(int argc, char **argv,
@@ -848,6 +915,9 @@ void igt_exit(void)
 {
 	igt_exit_called = true;
 
+	/* re-enstate the low mem killer in case we disabled it */
+	low_mem_killer_disable(false);
+
 	if (run_single_subtest && !run_single_subtest_found) {
 		igt_warn("Unknown subtest: %s\n", run_single_subtest);
 		exit(IGT_EXIT_INVALID);
-- 
2.1.1