Bug 693404 - Part 2: On Mac, purge MADV_FREE'd pages before reading RSS. r=khuey

toolkit/components/telemetry/TelemetryHistograms.h

@@ -84,6 +84,9 @@ HISTOGRAM(MEMORY_STORAGE_SQLITE, 1024, 512 * 1024, 50, EXPONENTIAL, "Memory used
 HISTOGRAM(MEMORY_IMAGES_CONTENT_USED_UNCOMPRESSED, 1024, 1024 * 1024, 50, EXPONENTIAL, "Memory used for uncompressed, in-use content images (KB)")
 HISTOGRAM(MEMORY_HEAP_ALLOCATED, 1024, 1024 * 1024, 50, EXPONENTIAL, "Heap memory allocated (KB)")
 HISTOGRAM(MEMORY_EXPLICIT, 1024, 1024 * 1024, 50, EXPONENTIAL, "Explicit memory allocations (KB)")
+#if defined(XP_MACOSX)
+HISTOGRAM(MEMORY_FREE_PURGED_PAGES_MS, 1, 1024, 10, EXPONENTIAL, "Time(ms) to purge MADV_FREE'd heap pages.")
+#endif
 #if defined(XP_WIN)
 HISTOGRAM(EARLY_GLUESTARTUP_READ_OPS, 1, 100, 12, LINEAR, "ProcessIoCounters.ReadOperationCount before glue startup")
 HISTOGRAM(EARLY_GLUESTARTUP_READ_TRANSFER, 1, 50 * 1024, 12, EXPONENTIAL, "ProcessIoCounters.ReadTransferCount before glue startup (KB)")

xpcom/base/nsMemoryReporterManager.cpp

@@ -42,6 +42,27 @@
 #include "nsMemoryReporterManager.h"
 #include "nsArrayEnumerator.h"
 #include "nsISimpleEnumerator.h"
+#include "mozilla/Telemetry.h"
+
+using namespace mozilla;
+
+#if defined(MOZ_MEMORY)
+#  if defined(XP_WIN) || defined(SOLARIS) || defined(ANDROID) || defined(XP_MACOSX)
+#    define HAVE_JEMALLOC_STATS 1
+#    include "jemalloc.h"
+#  elif defined(XP_LINUX)
+#    define HAVE_JEMALLOC_STATS 1
+#    include "jemalloc_types.h"
+// jemalloc is directly linked into firefox-bin; libxul doesn't link
+// with it.  So if we tried to use jemalloc_stats directly here, it
+// wouldn't be defined.  Instead, we don't include the jemalloc header
+// and weakly link against jemalloc_stats.
+extern "C" {
+extern void jemalloc_stats(jemalloc_stats_t* stats)
+  NS_VISIBILITY_DEFAULT __attribute__((weak));
+}
+#  endif  // XP_LINUX
+#endif  // MOZ_MEMORY
 
 #if defined(XP_LINUX) || defined(XP_MACOSX)
 
@@ -125,6 +146,20 @@ static PRInt64 GetVsize()
 
 static PRInt64 GetResident()
 {
+#ifdef HAVE_JEMALLOC_STATS
+    // If we're using jemalloc on Mac, we need to instruct jemalloc to purge
+    // the pages it has madvise(MADV_FREE)'d before we read our RSS.  The OS
+    // will take away MADV_FREE'd pages when there's memory pressure, so they
+    // shouldn't count against our RSS.
+    //
+    // Purging these pages shouldn't take more than 10ms or so, but we want to
+    // keep an eye on it since GetResident() is called on each Telemetry ping.
+    {
+      Telemetry::AutoTimer<Telemetry::MEMORY_FREE_PURGED_PAGES_MS> timer;
+      jemalloc_purge_freed_pages();
+    }
+#endif
+
     task_basic_info ti;
     return (PRInt64) (GetTaskBasicInfo(&ti) ? ti.resident_size : -1);
 }
@@ -255,24 +290,6 @@ NS_MEMORY_REPORTER_IMPLEMENT(Resident,
  ** at least -- on OSX, there are sometimes other zones in use).
  **/
 
-#if defined(MOZ_MEMORY)
-#  if defined(XP_WIN) || defined(SOLARIS) || defined(ANDROID) || defined(XP_MACOSX)
-#    define HAVE_JEMALLOC_STATS 1
-#    include "jemalloc.h"
-#  elif defined(XP_LINUX)
-#    define HAVE_JEMALLOC_STATS 1
-#    include "jemalloc_types.h"
-// jemalloc is directly linked into firefox-bin; libxul doesn't link
-// with it.  So if we tried to use jemalloc_stats directly here, it
-// wouldn't be defined.  Instead, we don't include the jemalloc header
-// and weakly link against jemalloc_stats.
-extern "C" {
-extern void jemalloc_stats(jemalloc_stats_t* stats)
-  NS_VISIBILITY_DEFAULT __attribute__((weak));
-}
-#  endif  // XP_LINUX
-#endif  // MOZ_MEMORY
-
 #if HAVE_JEMALLOC_STATS
 
 static PRInt64 GetHeapUnallocated()