Oilpan: Tweak a GC threshold to consider memory increase in PartitionAlloc

Source/platform/heap/ThreadState.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 497 matching lines @@
         return false;
 #if ENABLE(OILPAN)
     // The estimated size is updated when the main thread finishes lazy
     // sweeping. If this thread reaches here before the main thread finishes
     // lazy sweeping, the thread will use the estimated size of the last GC.
     size_t estimatedLiveObjectSize = Heap::estimatedLiveObjectSize();
     size_t allocatedObjectSize = Heap::allocatedObjectSize();
     // Heap::markedObjectSize() may be underestimated if any thread has not
     // finished completeSweep().
     size_t currentObjectSize = allocatedObjectSize + Heap::markedObjectSize() + WTF::Partitions::totalSizeOfCommittedPages();
-    // Schedule an idle GC if Oilpan has allocated more than 1 MB since
-    // the last GC and the current memory usage is >50% larger than
-    // the estimated live memory usage.
-    return allocatedObjectSize >= 1024 * 1024 && currentObjectSize > estimatedLiveObjectSize * 3 / 2;
+    return Heap::allocatedSpace() >= 1024 * 1024 // Oilpan has allocated >1 MB.
+        && currentObjectSize >= 1024 * 1024 // Oilpan or/and PartitionAlloc have allocated >1 MB since the last GC.

[sof, 2015/05/25 21:37:51]

If allocatedObjectSize >= 1024 * 1024, doesn't that imply that currentObjectSize
is larger than that threshold also?

[haraken, 2015/05/25 23:31:53]

Yes.

- allocatedObjectSize >= 1 MB implies currentObjectSize >= 1 MB.

- But in this CL, I'm using Heap::allocatedSpace() >= 1 MB, which is different
from allocatedObjectSize >= 1 MB. Note that Heap::allocatedSpace() is the total
size of memory allocated in Oilpan.

[sof, 2015/05/26 05:10:59]

Oops, quite right - I didn't pick the suffixes apart.

+        && currentObjectSize > estimatedLiveObjectSize * 3 / 2; // The current memory usage is >50% larger than the estimated live memory usage.
 #else
     return false;
 #endif
 }
 
 // TODO(haraken): We should improve the GC heuristics.
 // These heuristics affect performance significantly.
 bool ThreadState::shouldSchedulePreciseGC()
 {
     if (gcState() != NoGCScheduled)
         return false;
 #if ENABLE(OILPAN)
     return false;
 #else
     // The estimated size is updated when the main thread finishes lazy
     // sweeping. If this thread reaches here before the main thread finishes
     // lazy sweeping, the thread will use the estimated size of the last GC.
     size_t estimatedLiveObjectSize = Heap::estimatedLiveObjectSize();
     size_t allocatedObjectSize = Heap::allocatedObjectSize();
     // Heap::markedObjectSize() may be underestimated if any thread has not
     // finished completeSweep().
     size_t currentObjectSize = allocatedObjectSize + Heap::markedObjectSize() + WTF::Partitions::totalSizeOfCommittedPages();
-    // Schedule a precise GC if Oilpan has allocated more than 1 MB since
-    // the last GC and the current memory usage is >50% larger than
-    // the estimated live memory usage.
-    return allocatedObjectSize >= 1024 * 1024 && currentObjectSize > estimatedLiveObjectSize * 3 / 2;
+    return Heap::allocatedSpace() >= 1024 * 1024 // Oilpan has allocated >1 MB.
+        && currentObjectSize >= 1024 * 1024 // Oilpan or/and PartitionAlloc have allocated >1 MB since the last GC.

[sof, 2015/05/26 19:25:37]

Is this really true? totalSizeOfCommittedPages() doesn't measure a since-last-GC
amount, nor does markedObjectSize().

[haraken, 2015/05/27 00:39:00]

You're right; this comment is wrong. It should be:

  // The current memory usage in Oilpan and PartitionAlloc is >1 MB.

[sof, 2015/05/27 05:09:07]

Not just the comment is wrong; this seems like curve fitting to satisfy a
benchmark.

[haraken, 2015/05/27 05:50:03]

There would be various opinions, but IMO this is a threshold that has a
theoretical background (as explained in the old document). If Oilpan uses X MB,
PartitionAlloc uses Y MB and Oilpan has strong pointers to PartitionAlloc, it
would make sense to trigger Oilpan's GC based on X+Y.

+        && currentObjectSize > estimatedLiveObjectSize * 3 / 2; // The current memory usage is >50% larger than the estimated live memory usage.
 #endif
 }
 
 // TODO(haraken): We should improve the GC heuristics.
 // These heuristics affect performance significantly.
 bool ThreadState::shouldForceConservativeGC()
 {
     if (UNLIKELY(isGCForbidden()))
         return false;
 
     // The estimated size is updated when the main thread finishes lazy
     // sweeping. If this thread reaches here before the main thread finishes
     // lazy sweeping, the thread will use the estimated size of the last GC.
     size_t estimatedLiveObjectSize = Heap::estimatedLiveObjectSize();
     size_t allocatedObjectSize = Heap::allocatedObjectSize();
     // Heap::markedObjectSize() may be underestimated if any thread has not
     // finished completeSweep().
     size_t currentObjectSize = allocatedObjectSize + Heap::markedObjectSize() + WTF::Partitions::totalSizeOfCommittedPages();
     if (currentObjectSize >= 300 * 1024 * 1024) {
         // If we're consuming too much memory, trigger a conservative GC
         // aggressively. This is a safe guard to avoid OOM.
         return currentObjectSize > estimatedLiveObjectSize * 3 / 2;
     }
-    // Schedule a conservative GC if Oilpan has allocated more than 32 MB since
-    // the last GC and the current memory usage is >400% larger than
-    // the estimated live memory usage.
-    // TODO(haraken): 400% is too large. Lower the heap growing factor.
-    return allocatedObjectSize >= 32 * 1024 * 1024 && currentObjectSize > 5 * estimatedLiveObjectSize;
+    return Heap::allocatedSpace() >= 1024 * 1024 // Oilpan has allocated >1 MB.
+        && currentObjectSize >= 32 * 1024 * 1024 // Oilpan or/and PartitionAlloc have allocated >32 MB since the last GC.
+        && currentObjectSize > estimatedLiveObjectSize * 5; // The current memory usage is >400% larger than the estimated live memory usage. TODO(haraken): 400% is too large. Lower the heap growing factor.
 }
 
 void ThreadState::scheduleGCIfNeeded()
 {
     checkThread();
     // Allocation is allowed during sweeping, but those allocations should not
     // trigger nested GCs.
     if (isSweepingInProgress())
         return;
     ASSERT(!sweepForbidden());
@@ skipping 742 matching lines @@
         json->beginArray(it->key.ascii().data());
         for (size_t age = 0; age <= maxHeapObjectAge; ++age)
             json->pushInteger(it->value.ages[age]);
         json->endArray();
     }
     TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(TRACE_DISABLED_BY_DEFAULT("blink_gc"), statsName, this, json.release());
 }
 #endif
 
 } // namespace blink