[Tentaive patch for discussion] Add Purge+Suspend metrics as UMA.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 7c267b35fa6afcdd8e0997e16bafbd8f9635900c..d8aec6139cbebfaea714768ad661271de6572c3c 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1736,11 +1736,87 @@ void RenderThreadImpl::OnProcessPurgeAndSuspend() {
   ChildThreadImpl::OnProcessPurgeAndSuspend();
   if (is_renderer_suspended_)
     return;
+
+  blink_memory_stats_ = blink::WebMemoryStatistics::Get();
+  malloc_stats_ = base::trace_event::MallocDumpProvider::GetStatistics();
+  discardable_stats_ =
+      ChildThreadImpl::discardable_shared_memory_manager()->GetMemoryUsage();
+
+  // TODO(tasak): use MemoryCoordinator instead of NotifyMemoryPressure.
+  base::MemoryPressureListener::NotifyMemoryPressure(
+      base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL);
+  base::allocator::ReleaseFreeMemory();
+
+  // Since purging is not a synchronouse task (e.g. v8 GC, oilpan GC, ...),
+  // we need to wait until the task is finished. So wait 5 seconds and
+  // update purge+suspend uma histogram.
+  GetRendererScheduler()->DefaultTaskRunner()->PostDelayedTask(
+      FROM_HERE,
+      base::Bind(&RenderThreadImpl::OnDumpMemoryUsage, base::Unretained(this)),
+      base::TimeDelta::FromSeconds(5));
+
   // TODO(hajimehoshi): Implement purging e.g. cache (crbug/607077)
   is_renderer_suspended_ = true;
   renderer_scheduler_->SuspendRenderer();
 }
 
+// For purge+suspend, report memory usage diff by using UMA_HISTOGRAM.
+void RenderThreadImpl::OnDumpMemoryUsage() {
+  // If this renderer is resumed, we should not update uma.
+  if (!is_renderer_suspended_)
+    return;
+
+  blink::WebMemoryStatistics stats_after = blink::WebMemoryStatistics::Get();
+
+  base::trace_event::MallocStatistics malloc_stats_after =
+      base::trace_event::MallocDumpProvider::GetStatistics();
+
+  size_t discardable_usage_after =
+      ChildThreadImpl::discardable_shared_memory_manager()->GetMemoryUsage();
+
+  ssize_t diff = blink_memory_stats_.partitionAllocTotalAllocatedBytes -
+                 stats_after.partitionAllocTotalAllocatedBytes;
+  ssize_t total_diff = diff;
+  if (diff > 0)
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.PartitionAllocShrink", diff);
+  else
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.PartitionAllocGrowth", -diff);
+
+  diff = blink_memory_stats_.blinkGCTotalAllocatedBytes -
+         stats_after.blinkGCTotalAllocatedBytes;
+  if (diff > 0)
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.BlinkGCShrink", diff);
+  else
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.BlinkGCGrowth", -diff);
+
+  diff = malloc_stats_.allocated_objects_size -
+         malloc_stats_after.allocated_objects_size;
+  if (diff > 0)
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.MallocShrink", diff);
+  else
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.MallocGrowth", -diff);
+  total_diff += diff;
+
+  diff = malloc_stats_.resident_size - malloc_stats_after.resident_size;
+  if (diff > 0)
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.ResidentSizeShrink", diff);
+  else
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.ResidentSizeGrowth", -diff);
+  total_diff += diff;
+
+  diff = discardable_stats_ - discardable_usage_after;
+  if (diff > 0)
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.DiscardableShrink", diff);
+  else
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.DiscardableGrowth", -diff);
+  total_diff += diff;
+
+  if (total_diff > 0)
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.TotalShrink", total_diff);
+  else
+    UMA_HISTOGRAM_MEMORY_KB("PurgeAndSuspend.TotalGrowth", -total_diff);

[haraken, 2016/09/20 12:19:14]

isherman@: Is there any way to report a negative number to UMA?

[Ilya Sherman, 2016/09/21 21:15:48]

Yes, using a sparse histogram.  But, it's not very convenient for something like
what you're trying to do, where you want logarithmically scaled buckets.  So, I
don't really have a better suggestion than what you've implemented here, unless
you want to manually map from values to their corresponding bucket number --
sorry.

+}
+
 void RenderThreadImpl::OnCreateNewFrame(FrameMsg_NewFrame_Params params) {
   // Debug cases of https://crbug.com/626802.
   base::debug::SetCrashKeyValue("newframe_routing_id",