Expose ReleaseFreeMemory to free up memory on memory pressure or idle cleanup.

Source/wtf/Partitions.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 54 matching lines @@
 {
     // We could ASSERT here for a memory leak within the partition, but it leads
     // to very hard to diagnose ASSERTs, so it's best to leave leak checking for
     // the valgrind and heapcheck bots, which run without partitions.
     (void) m_renderingAllocator.shutdown();
     (void) m_objectModelAllocator.shutdown();
     (void) m_bufferAllocator.shutdown();
     (void) m_fastMallocAllocator.shutdown();
 }
 
+void Partitions::releaseFreeMemory()
+{
+    ASSERT(isMainThread());
+
+    spinLockLock(&getBufferPartition()->lock);

[haraken, 2015/06/03 11:39:00]

Can we move this lock into partitionPurgeMemory?

We want to write these as:

  getBufferPartition()->partitionPurgeMemory();
  getFastMallocPartition()->partitionPurgeMemory();
  ...;

[ssid, 2015/06/03 11:45:31]

1. PartitionRootBase is a struct and partitionPurgeMemory() is a function no in
the struct.
2. Lock is only needed in PartitionRootGeneric and not in PartitionRoot (both of
these extend PartitionRootBase).

I would have refactor partitionPurgeMemory() to move into the struct and have
two different implementation for it, one with lock and one without.

WDYT I should do here?

+    partitionPurgeMemory(getBufferPartition());
+    spinLockUnlock(&getBufferPartition()->lock);
+
+    spinLockLock(&getFastMallocPartition()->lock);
+    partitionPurgeMemory(getFastMallocPartition());
+    spinLockUnlock(&getFastMallocPartition()->lock);
+
+    partitionPurgeMemory(getObjectModelPartition());
+    partitionPurgeMemory(getRenderingPartition());
+}
+
 void Partitions::reportMemoryUsageHistogram()
 {
     static size_t supportedMaxSizeInMB = 4 * 1024;
     static size_t observedMaxSizeInMB = 0;
 
     if (!m_histogramEnumeration)
         return;
     // We only report the memory in the main thread.
     if (!isMainThread())
         return;
@@ skipping 15 matching lines @@
     // accessed only on the main thread.
     ASSERT(isMainThread());
 
     partitionDumpStatsGeneric(getFastMallocPartition(), "fast_malloc_partition", partitionStatsDumper);
     partitionDumpStatsGeneric(getBufferPartition(), "buffer_partition", partitionStatsDumper);
     partitionDumpStats(getObjectModelPartition(), "object_model_partition", partitionStatsDumper);
     partitionDumpStats(getRenderingPartition(), "rendering_partition", partitionStatsDumper);
 }
 
 } // namespace WTF