Bug 873284 - When a content process is running at high priority do not send memory-pressure events. r=khuey

dom/ipc/ProcessPriorityManager.cpp

@@ -102,8 +102,9 @@ class ParticularProcessPriorityManager;
  * can call StaticInit, but it won't do anything, and GetSingleton() will
  * return null.)
  *
- * ProcessPriorityManager::CurrentProcessIsForeground(), which can be called in
- * any process, is handled separately, by the ProcessPriorityManagerChild
+ * ProcessPriorityManager::CurrentProcessIsForeground() and
+ * ProcessPriorityManager::AnyProcessHasHighPriority() which can be called in
+ * any process, are handled separately, by the ProcessPriorityManagerChild
  * class.
  */
 class ProcessPriorityManagerImpl MOZ_FINAL
@@ -143,6 +144,11 @@ public:
   bool OtherProcessHasHighPriority(
     ParticularProcessPriorityManager* aParticularManager);
 
+  /**
+   * Does one of the child processes have priority FOREGROUND_HIGH?
+   */
+  bool ChildProcessHasHighPriority();
+
   /**
    * This must be called by a ParticularProcessPriorityManager when it changes
    * its priority.
@@ -191,6 +197,7 @@ public:
   NS_DECL_NSIOBSERVER
 
   bool CurrentProcessIsForeground();
+  bool CurrentProcessIsHighPriority();
 
 private:
   static StaticRefPtr<ProcessPriorityManagerChild> sSingleton;
@@ -540,6 +547,12 @@ ProcessPriorityManagerImpl::OtherProcessHasHighPriority(
   return mHighPriorityChildIDs.Count() > 0;
 }
 
+bool
+ProcessPriorityManagerImpl::ChildProcessHasHighPriority( void )
+{
+  return mHighPriorityChildIDs.Count() > 0;
+}
+
 void
 ProcessPriorityManagerImpl::NotifyProcessPriorityChanged(
   ParticularProcessPriorityManager* aParticularManager,
@@ -1204,6 +1217,13 @@ ProcessPriorityManagerChild::CurrentProcessIsForeground()
          mCachedPriority >= PROCESS_PRIORITY_FOREGROUND;
 }
 
+bool
+ProcessPriorityManagerChild::CurrentProcessIsHighPriority()
+{
+  return mCachedPriority == PROCESS_PRIORITY_UNKNOWN ||
+         mCachedPriority >= PROCESS_PRIORITY_FOREGROUND_HIGH;
+}
+
 /* static */ StaticAutoPtr<BackgroundProcessLRUPool>
 BackgroundProcessLRUPool::sSingleton;
 
@@ -1435,4 +1455,18 @@ ProcessPriorityManager::CurrentProcessIsForeground()
     CurrentProcessIsForeground();
 }
 
+/* static */ bool
+ProcessPriorityManager::AnyProcessHasHighPriority()
+{
+  ProcessPriorityManagerImpl* singleton =
+    ProcessPriorityManagerImpl::GetSingleton();
+
+  if (singleton) {
+    return singleton->ChildProcessHasHighPriority();
+  } else {
+    return ProcessPriorityManagerChild::Singleton()->
+      CurrentProcessIsHighPriority();
+  }
+}
+
 } // namespace mozilla

dom/ipc/ProcessPriorityManager.h

@@ -68,6 +68,12 @@ public:
    */
   static bool CurrentProcessIsForeground();
 
+  /**
+   * Returns true if one or more processes with FOREGROUND_HIGH priority are
+   * present, false otherwise.
+   */
+  static bool AnyProcessHasHighPriority();
+
   /**
    * Used to remove a ContentParent from background LRU pool when
    * it is destroyed or its priority changed from BACKGROUND to others.

widget/gonk/GonkMemoryPressureMonitoring.cpp

@@ -9,6 +9,7 @@
 #include "mozilla/FileUtils.h"
 #include "mozilla/Monitor.h"
 #include "mozilla/Preferences.h"
+#include "mozilla/ProcessPriorityManager.h"
 #include "mozilla/Services.h"
 #include "nsIObserver.h"
 #include "nsIObserverService.h"
@@ -169,7 +170,7 @@ public:
 
       // We use low-memory-no-forward because each process has its own watcher
       // and thus there is no need for the main process to forward this event.
-      rv = NS_DispatchMemoryPressure(MemPressure_New);
+      rv = DispatchMemoryPressure(MemPressure_New);
       NS_ENSURE_SUCCESS(rv, rv);
 
       // Manually check lowMemFd until we observe that memory pressure is over.
@@ -202,7 +203,7 @@ public:
         NS_ENSURE_SUCCESS(rv, rv);
 
         if (memoryPressure) {
-          rv = NS_DispatchMemoryPressure(MemPressure_Ongoing);
+          rv = DispatchMemoryPressure(MemPressure_Ongoing);
           NS_ENSURE_SUCCESS(rv, rv);
           continue;
         }
@@ -245,6 +246,21 @@ private:
     return NS_OK;
   }
 
+  /**
+   * Dispatch the specified memory pressure event unless a high-priority
+   * process is present. If a high-priority process is present then it's likely
+   * responding to an urgent event (an incoming call or message for example) so
+   * avoid wasting CPU time responding to low-memory events.
+   */
+  nsresult DispatchMemoryPressure(MemoryPressureState state)
+  {
+    if (ProcessPriorityManager::AnyProcessHasHighPriority()) {
+      return NS_OK;
+    }
+
+    return NS_DispatchMemoryPressure(state);
+  }
+
   Monitor mMonitor;
   uint32_t mPollMS;
   bool mShuttingDown;