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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/165458">165458</a></dd>
<dt>Author</dt> <dd>mhahnenberg@apple.com</dd>
<dt>Date</dt> <dd>2014-03-11 18:45:54 -0700 (Tue, 11 Mar 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>MarkedBlocks that are "full enough" shouldn't be swept after EdenCollections
https://bugs.webkit.org/show_bug.cgi?id=129920
Reviewed by Geoffrey Garen.
This patch introduces the notion of "retiring" MarkedBlocks. We retire a MarkedBlock
when the amount of free space in a MarkedBlock drops below a certain threshold.
Retired blocks are not considered for sweeping.
This is profitable because it reduces churn during sweeping. To build a free list,
we have to scan through each cell in a block. After a collection, all objects that
are live in the block will remain live until the next FullCollection, at which time
we un-retire all previously retired blocks. Thus, a small number of objects in a block
that die during each EdenCollection could cause us to do a disproportiante amount of
sweeping for how much free memory we get back.
This patch looks like a consistent ~2% progression on boyer and is neutral everywhere else.
* heap/Heap.h:
(JSC::Heap::didRetireBlockWithFreeListSize):
* heap/MarkedAllocator.cpp:
(JSC::MarkedAllocator::tryAllocateHelper):
(JSC::MarkedAllocator::removeBlock):
(JSC::MarkedAllocator::reset):
* heap/MarkedAllocator.h:
(JSC::MarkedAllocator::MarkedAllocator):
(JSC::MarkedAllocator::forEachBlock):
* heap/MarkedBlock.cpp:
(JSC::MarkedBlock::sweepHelper):
(JSC::MarkedBlock::clearMarksWithCollectionType):
(JSC::MarkedBlock::didRetireBlock):
* heap/MarkedBlock.h:
(JSC::MarkedBlock::willRemoveBlock):
(JSC::MarkedBlock::isLive):
* heap/MarkedSpace.cpp:
(JSC::MarkedSpace::clearNewlyAllocated):
(JSC::MarkedSpace::clearMarks):
* runtime/Options.h:</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedAllocatorcpp">trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedAllocatorh">trunk/Source/JavaScriptCore/heap/MarkedAllocator.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedBlockcpp">trunk/Source/JavaScriptCore/heap/MarkedBlock.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedBlockh">trunk/Source/JavaScriptCore/heap/MarkedBlock.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedSpacecpp">trunk/Source/JavaScriptCore/heap/MarkedSpace.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeOptionsh">trunk/Source/JavaScriptCore/runtime/Options.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -1,3 +1,44 @@
</span><ins>+2014-03-11 Mark Hahnenberg <mhahnenberg@apple.com>
+
+ MarkedBlocks that are "full enough" shouldn't be swept after EdenCollections
+ https://bugs.webkit.org/show_bug.cgi?id=129920
+
+ Reviewed by Geoffrey Garen.
+
+ This patch introduces the notion of "retiring" MarkedBlocks. We retire a MarkedBlock
+ when the amount of free space in a MarkedBlock drops below a certain threshold.
+ Retired blocks are not considered for sweeping.
+
+ This is profitable because it reduces churn during sweeping. To build a free list,
+ we have to scan through each cell in a block. After a collection, all objects that
+ are live in the block will remain live until the next FullCollection, at which time
+ we un-retire all previously retired blocks. Thus, a small number of objects in a block
+ that die during each EdenCollection could cause us to do a disproportiante amount of
+ sweeping for how much free memory we get back.
+
+ This patch looks like a consistent ~2% progression on boyer and is neutral everywhere else.
+
+ * heap/Heap.h:
+ (JSC::Heap::didRetireBlockWithFreeListSize):
+ * heap/MarkedAllocator.cpp:
+ (JSC::MarkedAllocator::tryAllocateHelper):
+ (JSC::MarkedAllocator::removeBlock):
+ (JSC::MarkedAllocator::reset):
+ * heap/MarkedAllocator.h:
+ (JSC::MarkedAllocator::MarkedAllocator):
+ (JSC::MarkedAllocator::forEachBlock):
+ * heap/MarkedBlock.cpp:
+ (JSC::MarkedBlock::sweepHelper):
+ (JSC::MarkedBlock::clearMarksWithCollectionType):
+ (JSC::MarkedBlock::didRetireBlock):
+ * heap/MarkedBlock.h:
+ (JSC::MarkedBlock::willRemoveBlock):
+ (JSC::MarkedBlock::isLive):
+ * heap/MarkedSpace.cpp:
+ (JSC::MarkedSpace::clearNewlyAllocated):
+ (JSC::MarkedSpace::clearMarks):
+ * runtime/Options.h:
+
</ins><span class="cx"> 2014-03-11 Andreas Kling <akling@apple.com>
</span><span class="cx">
</span><span class="cx"> Streamline PropertyTable for lookup-only access.
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedAllocatorcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -79,12 +79,12 @@
</span><span class="cx">
</span><span class="cx"> MarkedBlock::FreeList freeList = block->sweep(MarkedBlock::SweepToFreeList);
</span><span class="cx">
</span><del>- if (!freeList.head) {
- block->didConsumeEmptyFreeList();
</del><ins>+ double utilization = ((double)MarkedBlock::blockSize - (double)freeList.bytes) / (double)MarkedBlock::blockSize;
+ if (utilization >= Options::minMarkedBlockUtilization()) {
+ ASSERT(freeList.bytes || !freeList.head);
</ins><span class="cx"> m_blockList.remove(block);
</span><del>- m_blockList.push(block);
- if (!m_lastFullBlock)
- m_lastFullBlock = block;
</del><ins>+ m_retiredBlocks.push(block);
+ block->didRetireBlock(freeList);
</ins><span class="cx"> continue;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -211,9 +211,7 @@
</span><span class="cx"> if (m_nextBlockToSweep == block)
</span><span class="cx"> m_nextBlockToSweep = m_nextBlockToSweep->next();
</span><span class="cx">
</span><del>- if (block == m_lastFullBlock)
- m_lastFullBlock = m_lastFullBlock->prev();
-
</del><ins>+ block->willRemoveBlock();
</ins><span class="cx"> m_blockList.remove(block);
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -223,12 +221,9 @@
</span><span class="cx"> m_currentBlock = 0;
</span><span class="cx"> m_freeList = MarkedBlock::FreeList();
</span><span class="cx"> if (m_heap->operationInProgress() == FullCollection)
</span><del>- m_lastFullBlock = 0;
</del><ins>+ m_blockList.append(m_retiredBlocks);
</ins><span class="cx">
</span><del>- if (m_lastFullBlock)
- m_nextBlockToSweep = m_lastFullBlock->next() ? m_lastFullBlock->next() : m_lastFullBlock;
- else
- m_nextBlockToSweep = m_blockList.head();
</del><ins>+ m_nextBlockToSweep = m_blockList.head();
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> } // namespace JSC
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedAllocatorh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedAllocator.h (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedAllocator.h 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/heap/MarkedAllocator.h 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -54,8 +54,8 @@
</span><span class="cx"> MarkedBlock* m_currentBlock;
</span><span class="cx"> MarkedBlock* m_lastActiveBlock;
</span><span class="cx"> MarkedBlock* m_nextBlockToSweep;
</span><del>- MarkedBlock* m_lastFullBlock;
</del><span class="cx"> DoublyLinkedList<MarkedBlock> m_blockList;
</span><ins>+ DoublyLinkedList<MarkedBlock> m_retiredBlocks;
</ins><span class="cx"> size_t m_cellSize;
</span><span class="cx"> MarkedBlock::DestructorType m_destructorType;
</span><span class="cx"> Heap* m_heap;
</span><span class="lines">@@ -71,7 +71,6 @@
</span><span class="cx"> : m_currentBlock(0)
</span><span class="cx"> , m_lastActiveBlock(0)
</span><span class="cx"> , m_nextBlockToSweep(0)
</span><del>- , m_lastFullBlock(0)
</del><span class="cx"> , m_cellSize(0)
</span><span class="cx"> , m_destructorType(MarkedBlock::None)
</span><span class="cx"> , m_heap(0)
</span><span class="lines">@@ -136,6 +135,11 @@
</span><span class="cx"> next = block->next();
</span><span class="cx"> functor(block);
</span><span class="cx"> }
</span><ins>+
+ for (MarkedBlock* block = m_retiredBlocks.head(); block; block = next) {
+ next = block->next();
+ functor(block);
+ }
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> } // namespace JSC
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedBlockcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedBlock.cpp (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedBlock.cpp 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/heap/MarkedBlock.cpp 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -129,6 +129,7 @@
</span><span class="cx"> // Happens when a block transitions to fully allocated.
</span><span class="cx"> ASSERT(sweepMode == SweepToFreeList);
</span><span class="cx"> return FreeList();
</span><ins>+ case Retired:
</ins><span class="cx"> case Allocated:
</span><span class="cx"> RELEASE_ASSERT_NOT_REACHED();
</span><span class="cx"> return FreeList();
</span><span class="lines">@@ -226,11 +227,16 @@
</span><span class="cx"> #if ENABLE(GGC)
</span><span class="cx"> m_rememberedSet.clearAll();
</span><span class="cx"> #endif
</span><ins>+ // This will become true at the end of the mark phase. We set it now to
+ // avoid an extra pass to do so later.
+ m_state = Marked;
+ return;
</ins><span class="cx"> }
</span><span class="cx">
</span><del>- // This will become true at the end of the mark phase. We set it now to
- // avoid an extra pass to do so later.
- m_state = Marked;
</del><ins>+ ASSERT(collectionType == EdenCollection);
+ // If a block was retired then there's no way an EdenCollection can un-retire it.
+ if (m_state != Retired)
+ m_state = Marked;
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void MarkedBlock::lastChanceToFinalize()
</span><span class="lines">@@ -258,4 +264,27 @@
</span><span class="cx"> return sweep(SweepToFreeList);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+void MarkedBlock::didRetireBlock(const FreeList& freeList)
+{
+ HEAP_LOG_BLOCK_STATE_TRANSITION(this);
+ FreeCell* head = freeList.head;
+
+ // Currently we don't notify the Heap that we're giving up on this block.
+ // The Heap might be able to make a better decision about how many bytes should
+ // be allocated before the next collection if it knew about this retired block.
+ // On the other hand we'll waste at most 10% of our Heap space between FullCollections
+ // and only under heavy fragmentation.
+
+ // We need to zap the free list when retiring a block so that we don't try to destroy
+ // previously destroyed objects when we re-sweep the block in the future.
+ FreeCell* next;
+ for (FreeCell* current = head; current; current = next) {
+ next = current->next;
+ reinterpret_cast<JSCell*>(current)->zap();
+ }
+
+ ASSERT(m_state == FreeListed);
+ m_state = Retired;
+}
+
</ins><span class="cx"> } // namespace JSC
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedBlockh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedBlock.h (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedBlock.h 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/heap/MarkedBlock.h 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -177,6 +177,8 @@
</span><span class="cx"> void clearNewlyAllocated(const void*);
</span><span class="cx">
</span><span class="cx"> bool needsSweeping();
</span><ins>+ void didRetireBlock(const FreeList&);
+ void willRemoveBlock();
</ins><span class="cx">
</span><span class="cx"> template <typename Functor> void forEachCell(Functor&);
</span><span class="cx"> template <typename Functor> void forEachLiveCell(Functor&);
</span><span class="lines">@@ -187,7 +189,7 @@
</span><span class="cx"> private:
</span><span class="cx"> static const size_t atomAlignmentMask = atomSize - 1; // atomSize must be a power of two.
</span><span class="cx">
</span><del>- enum BlockState { New, FreeListed, Allocated, Marked };
</del><ins>+ enum BlockState { New, FreeListed, Allocated, Marked, Retired };
</ins><span class="cx"> template<DestructorType> FreeList sweepHelper(SweepMode = SweepOnly);
</span><span class="cx">
</span><span class="cx"> typedef char Atom[atomSize];
</span><span class="lines">@@ -282,6 +284,11 @@
</span><span class="cx"> m_weakSet.reap();
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ inline void MarkedBlock::willRemoveBlock()
+ {
+ ASSERT(m_state != Retired);
+ }
+
</ins><span class="cx"> inline void MarkedBlock::didConsumeFreeList()
</span><span class="cx"> {
</span><span class="cx"> HEAP_LOG_BLOCK_STATE_TRANSITION(this);
</span><span class="lines">@@ -405,6 +412,7 @@
</span><span class="cx"> case Allocated:
</span><span class="cx"> return true;
</span><span class="cx">
</span><ins>+ case Retired:
</ins><span class="cx"> case Marked:
</span><span class="cx"> return m_marks.get(atomNumber(cell)) || (m_newlyAllocated && isNewlyAllocated(cell));
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedSpacecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedSpace.cpp (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedSpace.cpp 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/heap/MarkedSpace.cpp 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -317,12 +317,6 @@
</span><span class="cx"> #endif
</span><span class="cx"> }
</span><span class="cx">
</span><del>-#ifndef NDEBUG
-struct VerifyMarked : MarkedBlock::VoidFunctor {
- void operator()(MarkedBlock* block) { ASSERT(block->needsSweeping()); }
-};
-#endif
-
</del><span class="cx"> void MarkedSpace::clearMarks()
</span><span class="cx"> {
</span><span class="cx"> if (m_heap->operationInProgress() == EdenCollection) {
</span><span class="lines">@@ -330,9 +324,6 @@
</span><span class="cx"> m_blocksWithNewObjects[i]->clearMarks();
</span><span class="cx"> } else
</span><span class="cx"> forEachBlock<ClearMarks>();
</span><del>-#ifndef NDEBUG
- forEachBlock<VerifyMarked>();
-#endif
</del><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void MarkedSpace::willStartIterating()
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeOptionsh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/Options.h (165457 => 165458)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/Options.h 2014-03-12 00:19:40 UTC (rev 165457)
+++ trunk/Source/JavaScriptCore/runtime/Options.h 2014-03-12 01:45:54 UTC (rev 165458)
</span><span class="lines">@@ -238,6 +238,7 @@
</span><span class="cx"> v(unsigned, opaqueRootMergeThreshold, 1000) \
</span><span class="cx"> v(double, minHeapUtilization, 0.8) \
</span><span class="cx"> v(double, minCopiedBlockUtilization, 0.9) \
</span><ins>+ v(double, minMarkedBlockUtilization, 0.9) \
</ins><span class="cx"> \
</span><span class="cx"> v(bool, forceWeakRandomSeed, false) \
</span><span class="cx"> v(unsigned, forcedWeakRandomSeed, 0) \
</span></span></pre>
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