Add support for the cgroups config we have in chromeos

base/process_linux.cc

Index: base/process_linux.cc
diff --git a/base/process_linux.cc b/base/process_linux.cc
index 14c24240e38288251d925cca4c520695bb1a0da8..9764f02a0f58c52fed32a365736ca46b57ceb8b7 100644
--- a/base/process_linux.cc
+++ b/base/process_linux.cc
@@ -7,7 +7,20 @@
 #include <errno.h>
 #include <sys/resource.h>
 
+#include "base/file_util.h"
 #include "base/logging.h"
+#include "base/stringprintf.h"
+
+#if defined(OS_CHROMEOS)
+static bool use_cgroups = false;
+static bool cgroups_inited = false;
+static const char kForegroundTasks[] =
+    "/tmp/cgroup/cpu/chrome_renderers/foreground/tasks";
+static const char kBackgroundTasks[] =
+    "/tmp/cgroup/cpu/chrome_renderers/background/tasks";
+static FilePath foreground_tasks;
+static FilePath background_tasks;
+#endif
 
 namespace base {
 
@@ -28,6 +41,53 @@ bool Process::IsProcessBackgrounded() const {
 bool Process::SetProcessBackgrounded(bool background) {
   DCHECK(process_);
 
+#if defined(OS_CHROMEOS)
+  // Check for cgroups files. ChromeOS supports these by default. It creates
+  // a cgroup mount in /tmp/cgroup and then configures two cpu task groups,
+  // one contains at most a single foreground renderer and the other contains
+  // all background renderers. This allows us to limit the impact of background
+  // renderers on foreground ones to a greater level than simple renicing.
+  if (!cgroups_inited) {
+    cgroups_inited = true;
+    foreground_tasks = FilePath(kForegroundTasks);
+    background_tasks = FilePath(kBackgroundTasks);
+    file_util::FileSystemType foreground_type;
+    file_util::FileSystemType background_type;
+    use_cgroups =
+        file_util::GetFileSystemType(foreground_tasks, &foreground_type) &&
+        file_util::GetFileSystemType(background_tasks, &background_type) &&
+        foreground_type == file_util::FILE_SYSTEM_CGROUP &&
+        background_type == file_util::FILE_SYSTEM_CGROUP;
+  }
+
+  if (use_cgroups) {
+    if (background) {
+      std::string pid = StringPrintf("%d", process_);
+      if (file_util::WriteFile(background_tasks, pid.c_str(), pid.size()) > 0) {
+        // With cgroups there's no real notion of priority as an int, but this
+        // will ensure we only move renderers back to the foreground group
+        // if we've ever put them in the background one.
+        saved_priority_ = 0;
+        return true;
+      } else {
+        return false;
+      }
+    } else {
+      if (saved_priority_ == kUnsetProcessPriority) {
+        // Can't restore if we were never backgrounded.
+        return false;
+      }
+      std::string pid = StringPrintf("%d", process_);
+      if (file_util::WriteFile(foreground_tasks, pid.c_str(), pid.size()) > 0) {
+        saved_priority_ = kUnsetProcessPriority;
+        return true;
+      } else {
+        return false;
+      }
+    }
+  }
+#endif // OS_CHROMEOS
+
   if (background) {
     // We won't be able to raise the priority if we don't have the right rlimit.
     // The limit may be adjusted in /etc/security/limits.conf for PAM systems.