lib: Do two writes to /proc/sys/vm/drop_caches again

The drop_caches sysctl has a max value of 4, so writing 7 to it just
fails. Avoid the earlier two-writes problem by opening the fd twice.

v2: Don't lseek(), open() twice. (Chris)

Signed-off-by: Petri Latvala <petri.latvala@intel.com>

1 files changed, 14 insertions, 2 deletions

diff --git a/lib/intel_os.c b/lib/intel_os.c
index b9f970df..0f9af634 100644
--- a/lib/intel_os.c
+++ b/lib/intel_os.c
@@ -296,14 +296,26 @@ void intel_purge_vm_caches(void)
 	int fd;
 
 	fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
+	if (fd >= 0) {
+		/* BIT(2): Be quiet. Cannot be combined with other operations,
+		 * the sysctl has a max value of 4.
+		 */
+		igt_ignore_warn(write(fd, "4\n", 2));
+		close(fd);
+	}
+
+	/* Reset write position back to start. Do as a seperate write to keep
+	 * the stages segregated and avoid failure from the squelching stopping
+	 * the purge.
+	 */
+	fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
 	if (fd < 0)
 		return;
 
 	/* BIT(0): Drop page cache
 	 * BIT(1): Drop slab cache
-	 * BIT(2): Be quiet in future
 	 */
-	igt_ignore_warn(write(fd, "7\n", 2));
+	igt_ignore_warn(write(fd, "3\n", 2));
 	close(fd);
 }