1 files changed, 78 insertions, 0 deletions
diff --git a/hal/linux/LinuxProcessPriority.cpp b/hal/linux/LinuxProcessPriority.cpp
new file mode 100644
index 0000000000..a0f72a4f38
--- /dev/null
+++ b/hal/linux/LinuxProcessPriority.cpp
@@ -0,0 +1,78 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Hal.h"
+#include "HalLog.h"
+
+#include "mozilla/Sprintf.h"
+#include "mozilla/Unused.h"
+
+#include <fcntl.h>
+#include <unistd.h>
+
+using namespace mozilla::hal;
+
+namespace mozilla::hal_impl {
+
+/* The Linux OOM score is a value computed by the kernel ranging between 0 and
+ * 1000 and indicating how likely is a process to be killed when memory is
+ * tight. The larger the value the more likely a process is to be killed. The
+ * score is computed based on the amount of memory used plus an adjustment
+ * value. We chose our adjustment values to make it likely that processes are
+ * killed in the following order:
+ *
+ * 1. preallocated processes
+ * 2. background processes
+ * 3. background processes playing video (but no audio)
+ * 4. foreground processes or processes playing or recording audio
+ * 5. the parent process
+ *
+ * At the time of writing (2022) the base score for a process consuming very
+ * little memory seems to be around ~667. Our adjustments are thus designed
+ * to ensure this order starting from a 667 baseline but trying not to go too
+ * close to the 1000 limit where they would be clamped. */
+
+const uint32_t kParentOomScoreAdjust = 0;
+const uint32_t kForegroundOomScoreAdjust = 100;
+const uint32_t kBackgroundPerceivableOomScoreAdjust = 133;
+const uint32_t kBackgroundOomScoreAdjust = 167;
+const uint32_t kPreallocOomScoreAdjust = 233;
+
+static uint32_t OomScoreAdjForPriority(ProcessPriority aPriority) {
+  switch (aPriority) {
+    case PROCESS_PRIORITY_BACKGROUND:
+      return kBackgroundOomScoreAdjust;
+    case PROCESS_PRIORITY_BACKGROUND_PERCEIVABLE:
+      return kBackgroundPerceivableOomScoreAdjust;
+    case PROCESS_PRIORITY_PREALLOC:
+      return kPreallocOomScoreAdjust;
+    case PROCESS_PRIORITY_FOREGROUND:
+      return kForegroundOomScoreAdjust;
+    default:
+      return kParentOomScoreAdjust;
+  }
+}
+
+void SetProcessPriority(int aPid, ProcessPriority aPriority) {
+  HAL_LOG("LinuxProcessPriority - SetProcessPriority(%d, %s)\n", aPid,
+          ProcessPriorityToString(aPriority));
+
+  uint32_t oomScoreAdj = OomScoreAdjForPriority(aPriority);
+
+  char path[32] = {};
+  SprintfLiteral(path, "/proc/%d/oom_score_adj", aPid);
+
+  char oomScoreAdjStr[11] = {};
+  SprintfLiteral(oomScoreAdjStr, "%d", oomScoreAdj);
+
+  int fd = open(path, O_WRONLY);
+  if (fd < 0) {
+    return;
+  }
+  const size_t len = strlen(oomScoreAdjStr);
+  Unused << write(fd, oomScoreAdjStr, len);
+  Unused << close(fd);
+}
+
+}  // namespace mozilla::hal_impl