Add simple malloc statistics and metrics

Add some basic statistics for allocated memory based on mallinfo(),
and use that to define two metrics:

 usedAfterOverview: bytes used after the overview is shown once
 leakedAfterOverview: additional bytes used when the overview is
   shown a second time.

https://bugzilla.gnome.org/show_bug.cgi?id=618189

js/perf/core.js

@@ -12,7 +12,9 @@ let METRIC_DESCRIPTIONS = {
     overviewLatencyFirst: "Time to first frame after triggering overview, first time",
     overviewFramesFirst: "Frames displayed when going to overview, first time",
     overviewLatencySubsequent: "Time to first frame after triggering overview, second time",
-    overviewFramesSubsequent: "Frames displayed when going to overview, second time"
+    overviewFramesSubsequent: "Frames displayed when going to overview, second time",
+    usedAfterOverview: "Malloc'ed bytes after the overview is shown once",
+    leakedAfterOverview: "Additional malloc'ed bytes the second time the overview is shown"
 };
 
 let METRICS = {
@@ -21,6 +23,7 @@ let METRICS = {
 function run() {
     Scripting.defineScriptEvent("overviewShowStart", "Starting to show the overview");
     Scripting.defineScriptEvent("overviewShowDone", "Overview finished showing");
+    Scripting.defineScriptEvent("afterShowHide", "After a show/hide cycle for the overview");
 
     yield Scripting.sleep(1000);
     yield Scripting.waitLeisure();
@@ -29,8 +32,14 @@ function run() {
         Main.overview.show();
         yield Scripting.waitLeisure();
         Scripting.scriptEvent('overviewShowDone');
+
         Main.overview.hide();
         yield Scripting.waitLeisure();
+
+        global.gc();
+        yield Scripting.sleep(1000);
+        Scripting.collectStatistics();
+        Scripting.scriptEvent('afterShowHide');
     }
 }
 
@@ -38,6 +47,9 @@ let showingOverview = false;
 let overviewShowStart;
 let overviewFrames;
 let overviewLatency;
+let mallocUsedSize = 0;
+let overviewShowCount = 0;
+let firstOverviewUsedSize;
 
 function script_overviewShowStart(time) {
     showingOverview = true;
@@ -48,7 +60,9 @@ function script_overviewShowStart(time) {
 function script_overviewShowDone(time) {
     showingOverview = false;
 
-    if (!('overviewLatencyFirst' in METRICS)) {
+    overviewShowCount++;
+
+    if (overviewShowCount == 1) {
         METRICS.overviewLatencyFirst = overviewLatency;
         METRICS.overviewFramesFirst = overviewFrames;
     } else {
@@ -57,6 +71,18 @@ function script_overviewShowDone(time) {
     }
 }
 
+function script_afterShowHide(time) {
+    if (overviewShowCount == 1) {
+        METRICS.usedAfterOverview = mallocUsedSize;
+    } else {
+        METRICS.leakedAfterOverview = mallocUsedSize - METRICS.usedAfterOverview;
+    }
+}
+
+function malloc_usedSize(time, bytes) {
+    mallocUsedSize = bytes;
+}
+
 function clutter_stagePaintDone(time) {
     if (showingOverview) {
         if (overviewFrames == 0)

js/ui/scripting.js

@@ -94,6 +94,15 @@ function scriptEvent(name) {
     Shell.PerfLog.get_default().event("script." + name);
 }
 
+/**
+ * collectStatistics
+ *
+ * Convenience function to trigger statistics collection
+ */
+function collectStatistics() {
+    Shell.PerfLog.get_default().collect_statistics();
+}
+
 function _step(g, finish, onError) {
     try {
         let waitFunction = g.next();

src/gnome-shell-plugin.c

@@ -38,12 +38,14 @@
 #include <gjs/gjs.h>
 #include <girepository.h>
 #include <gmodule.h>
+#include <malloc.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "display.h"
 
 #include "shell-global-private.h"
+#include "shell-perf-log.h"
 #include "shell-wm.h"
 #include "st.h"
 
@@ -232,6 +234,50 @@ settings_notify_cb (GtkSettings *settings,
   update_font_options (settings);
 }
 
+static void
+malloc_statistics_callback (ShellPerfLog *perf_log,
+                            gpointer      data)
+{
+  struct mallinfo info = mallinfo ();
+
+  shell_perf_log_update_statistic_i (perf_log,
+                                     "malloc.arenaSize",
+                                     info.arena);
+  shell_perf_log_update_statistic_i (perf_log,
+                                     "malloc.mmapSize",
+                                     info.hblkhd);
+  shell_perf_log_update_statistic_i (perf_log,
+                                     "malloc.usedSize",
+                                     info.uordblks);
+}
+
+static void
+add_statistics (GnomeShellPlugin *shell_plugin)
+{
+  ShellPerfLog *perf_log = shell_perf_log_get_default ();
+
+  /* For probably historical reasons, mallinfo() defines the returned values,
+   * even those in bytes as int, not size_t. We're determined not to use
+   * more than 2G of malloc'ed memory, so are OK with that.
+   */
+  shell_perf_log_define_statistic (perf_log,
+                                   "malloc.arenaSize",
+                                   "Amount of memory allocated by malloc() with brk(), in bytes",
+                                   "i");
+  shell_perf_log_define_statistic (perf_log,
+                                   "malloc.mmapSize",
+                                   "Amount of memory allocated by malloc() with mmap(), in bytes",
+                                   "i");
+  shell_perf_log_define_statistic (perf_log,
+                                   "malloc.usedSize",
+                                   "Amount of malloc'ed memory currently in use",
+                                   "i");
+
+  shell_perf_log_add_statistics_callback (perf_log,
+                                          malloc_statistics_callback,
+                                          NULL, NULL);
+}
+
 static void
 gnome_shell_plugin_start (MutterPlugin *plugin)
 {
@@ -280,6 +326,8 @@ gnome_shell_plugin_start (MutterPlugin *plugin)
   _shell_global_set_plugin (global, MUTTER_PLUGIN(shell_plugin));
   _shell_global_set_gjs_context (global, shell_plugin->gjs_context);
 
+  add_statistics (shell_plugin);
+
   if (!gjs_context_eval (shell_plugin->gjs_context,
                          "const Main = imports.ui.main; Main.start();",
                          -1,