Refine memory accounting in ImageDecodingStore for discardable entries.

Source/platform/graphics/ImageDecodingStore.cpp

 /*
  * Copyright (C) 2012 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 14 matching lines @@
 
 #include "config.h"
 #include "platform/graphics/ImageDecodingStore.h"
 
 #include "platform/TraceEvent.h"
 
 namespace WebCore {
 
 namespace {
 
+// Allow up to 128 non-accounted discardable entries. Non-accounted entries are
+// entries that do not contribute to the memory usage of the cache.
+static const size_t maxNonAccountedDiscardableEntries = 128;
 // 32MB memory limit for cache.
 static const size_t defaultCacheLimitInBytes = 32768 * 1024;
 static ImageDecodingStore* s_instance = 0;
 static bool s_imageCachingEnabled = true;
 
 static void setInstance(ImageDecodingStore* imageDecodingStore)
 {
     delete s_instance;
     s_instance = imageDecodingStore;
 }
 
 } // namespace
 
 ImageDecodingStore::ImageDecodingStore()
-    : m_cacheLimitInBytes(defaultCacheLimitInBytes)
+    : m_discardableEntriesCount(0)
+    , m_cacheLimitInBytes(defaultCacheLimitInBytes)
     , m_memoryUsageInBytes(0)
 {
 }
 
 ImageDecodingStore::~ImageDecodingStore()
 {
 #ifndef NDEBUG
     setCacheLimitInBytes(0);
     ASSERT(!m_imageCacheMap.size());
     ASSERT(!m_decoderCacheMap.size());
@@ skipping 278 matching lines @@
         return false;
     }
     cacheEntry->incrementUseCount();
     *cachedImage = image;
     return true;
 }
 
 template<class T, class U, class V>
 void ImageDecodingStore::insertCacheInternal(PassOwnPtr<T> cacheEntry, U* cacheMap, V* identifierMap)
 {
-    // Usage of discardable memory is not counted because we want to use more
-    // than the cache limit allows. Cache limit only applies to non-discardable
-    // objects.
-    if (!cacheEntry->isDiscardable())
+    if (cacheEntry->isDiscardable()) {
+        ++m_discardableEntriesCount;
+        if (m_discardableEntriesCount <= maxNonAccountedDiscardableEntries)
+            cacheEntry->disableAccounting();
+    }
+    if (cacheEntry->isAccountingEnabled())
         incrementMemoryUsage(cacheEntry->memoryUsageInBytes());
 
     // m_orderedCacheList is used to support LRU operations to reorder cache
     // entries quickly.
     m_orderedCacheList.append(cacheEntry.get());
 
     typename U::KeyType key = cacheEntry->cacheKey();
     typename V::AddResult result = identifierMap->add(cacheEntry->generator(), typename V::MappedType());
     result.iterator->value.add(key);
     cacheMap->add(key, cacheEntry);
 
     TRACE_COUNTER1("webkit", "ImageDecodingStoreMemoryUsageBytes", m_memoryUsageInBytes);
     TRACE_COUNTER1("webkit", "ImageDecodingStoreNumOfImages", m_imageCacheMap.size());
     TRACE_COUNTER1("webkit", "ImageDecodingStoreNumOfDecoders", m_decoderCacheMap.size());
 }
 
 template<class T, class U, class V>
 void ImageDecodingStore::removeFromCacheInternal(const T* cacheEntry, U* cacheMap, V* identifierMap, Vector<OwnPtr<CacheEntry> >* deletionList)
 {
-    if (!cacheEntry->isDiscardable())
+    if (cacheEntry->isDiscardable()) {
+        ASSERT(m_discardableEntriesCount > 0);
+        --m_discardableEntriesCount;
+    }
+    if (cacheEntry->isAccountingEnabled())
         decrementMemoryUsage(cacheEntry->memoryUsageInBytes());
 
     // Remove entry from identifier map.
     typename V::iterator iter = identifierMap->find(cacheEntry->generator());
     ASSERT(iter != identifierMap->end());
     iter->value.remove(cacheEntry->cacheKey());
     if (!iter->value.size())
         identifierMap->remove(iter);
 
     // Remove entry from cache map.
@@ skipping 35 matching lines @@
     }
 }
 
 void ImageDecodingStore::removeFromCacheListInternal(const Vector<OwnPtr<CacheEntry> >& deletionList)
 {
     for (size_t i = 0; i < deletionList.size(); ++i)
         m_orderedCacheList.remove(deletionList[i].get());
 }
 
 } // namespace WebCore