Bug 944842 - Record and warn about swapping during builds; r=glandium

--HG--
extra : rebase_source : 3930a423514b5422ba23129b4da2a38f863bffbe
extra : amend_source : a9368fce73d02dc1f5073e652e4ab0b33f4c0a21

python/mozbuild/mozbuild/controller/building.py

@@ -453,6 +453,28 @@ class BuildMonitor(MozbuildObject):
 
         return finder_percent > 25, finder_percent
 
+    def have_excessive_swapping(self):
+        """Determine whether there was excessive swapping during the build.
+
+        Returns a tuple of (excessive, swap_in, swap_out). All values are None
+        if no swap information is available.
+        """
+        if not self.have_resource_usage:
+            return None, None, None
+
+        swap_in = sum(m.swap.sin for m in self.resources.measurements)
+        swap_out = sum(m.swap.sout for m in self.resources.measurements)
+
+        # The threshold of 1024 MB has been arbitrarily chosen.
+        #
+        # Choosing a proper value that is ideal for everyone is hard. We will
+        # likely iterate on the logic until people are generally satisfied.
+        # If a value is too low, the eventual warning produced does not carry
+        # much meaning. If the threshold is too high, people may not see the
+        # warning and the warning will thus be ineffective.
+        excessive = swap_in > 512 * 1048576 or swap_out > 512 * 1048576
+        return excessive, swap_in, swap_out
+
     @property
     def have_resource_usage(self):
         """Whether resource usage is available."""
@@ -480,6 +502,14 @@ class BuildMonitor(MozbuildObject):
         self._log_resource_usage('Overall system resources', 'resource_usage',
             self.end_time - self.start_time, cpu_percent, cpu_times, io)
 
+        excessive, sin, sout = self.have_excessive_swapping()
+        if excessive is not None and (sin or sout):
+            sin /= 1048576
+            sout /= 1048576
+            self.log(logging.WARNING, 'swap_activity',
+                {'sin': sin, 'sout': sout},
+                'Swap in/out (MB): {sin}/{sout}')
+
         o = dict(
             version=1,
             start=self.start_time,

python/mozbuild/mozbuild/mach_commands.py

@@ -49,6 +49,23 @@ Preferences.
 ===================
 '''.strip()
 
+EXCESSIVE_SWAP_MESSAGE = '''
+===================
+PERFORMANCE WARNING
+
+Your machine experienced a lot of swap activity during the build. This is
+possibly a sign that your machine doesn't have enough physical memory or
+not enough available memory to perform the build. It's also possible some
+other system activity during the build is to blame.
+
+If you feel this message is not appropriate for your machine configuration,
+please file a Core :: Build Config bug at
+https://bugzilla.mozilla.org/enter_bug.cgi?product=Core&component=Build%20Config
+and tell us about your machine and build configuration so we can adjust the
+warning heuristic.
+===================
+'''
+
 
 class TerminalLoggingHandler(logging.Handler):
     """Custom logging handler that works with terminal window dressing.
@@ -424,6 +441,10 @@ class Build(MachCommandBase):
             print('Your build was successful!')
 
         if monitor.have_resource_usage:
+            excessive, swap_in, swap_out = monitor.have_excessive_swapping()
+            if excessive:
+                print(EXCESSIVE_SWAP_MESSAGE)
+
             print('To view resource usage of the build, run |mach '
                 'resource-usage|.')