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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/196186">196186</a></dd>
<dt>Author</dt> <dd>sbarati@apple.com</dd>
<dt>Date</dt> <dd>2016-02-05 13:34:27 -0800 (Fri, 05 Feb 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>bmalloc: largeMax calculation is wrong on iOS
https://bugs.webkit.org/show_bug.cgi?id=153923
Reviewed by Mark Lam.
Our number for largeMax was larger than what we had
space to actually allocate inside the LargeChunk. This made
it so that we would allocate a large object for something
that really should be extra large. Previously:
largeMax + sizeof(LargeChunk) > 1MB
which meant that when we would grow() to accommodate an allocation
of a particular size inside a LargeObject despite the fact that
the allocation size would be too large to actually fit in the LargeObject.
This would manifest when we had an allocation size in the range:
1MB - sizeof(LargeChunk) < allocation size < largeMax
We fix this bug by being precise in our calculation of largeMax
instead of just assuming largeChunkSize * 99/100 is enough
space for the metadata.
* bmalloc/LargeChunk.h:
(bmalloc::LargeChunk::get):
* bmalloc/Sizes.h:</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourcebmallocChangeLog">trunk/Source/bmalloc/ChangeLog</a></li>
<li><a href="#trunkSourcebmallocbmallocLargeChunkh">trunk/Source/bmalloc/bmalloc/LargeChunk.h</a></li>
<li><a href="#trunkSourcebmallocbmallocSizesh">trunk/Source/bmalloc/bmalloc/Sizes.h</a></li>
<li><a href="#trunkSourcebmallocbmallocVMHeapcpp">trunk/Source/bmalloc/bmalloc/VMHeap.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourcebmallocChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/bmalloc/ChangeLog (196185 => 196186)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/bmalloc/ChangeLog 2016-02-05 21:22:39 UTC (rev 196185)
+++ trunk/Source/bmalloc/ChangeLog 2016-02-05 21:34:27 UTC (rev 196186)
</span><span class="lines">@@ -1,3 +1,29 @@
</span><ins>+2016-02-05 Saam barati <sbarati@apple.com>
+
+ bmalloc: largeMax calculation is wrong on iOS
+ https://bugs.webkit.org/show_bug.cgi?id=153923
+
+ Reviewed by Mark Lam.
+
+ Our number for largeMax was larger than what we had
+ space to actually allocate inside the LargeChunk. This made
+ it so that we would allocate a large object for something
+ that really should be extra large. Previously:
+ largeMax + sizeof(LargeChunk) > 1MB
+ which meant that when we would grow() to accommodate an allocation
+ of a particular size inside a LargeObject despite the fact that
+ the allocation size would be too large to actually fit in the LargeObject.
+ This would manifest when we had an allocation size in the range:
+ 1MB - sizeof(LargeChunk) < allocation size < largeMax
+
+ We fix this bug by being precise in our calculation of largeMax
+ instead of just assuming largeChunkSize * 99/100 is enough
+ space for the metadata.
+
+ * bmalloc/LargeChunk.h:
+ (bmalloc::LargeChunk::get):
+ * bmalloc/Sizes.h:
+
</ins><span class="cx"> 2016-01-31 Dan Bernstein <mitz@apple.com>
</span><span class="cx">
</span><span class="cx"> [Cocoa] Remove unused definition of HAVE_HEADER_DETECTION_H
</span></span></pre></div>
<a id="trunkSourcebmallocbmallocLargeChunkh"></a>
<div class="modfile"><h4>Modified: trunk/Source/bmalloc/bmalloc/LargeChunk.h (196185 => 196186)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/bmalloc/bmalloc/LargeChunk.h 2016-02-05 21:22:39 UTC (rev 196185)
+++ trunk/Source/bmalloc/bmalloc/LargeChunk.h 2016-02-05 21:34:27 UTC (rev 196186)
</span><span class="lines">@@ -78,6 +78,9 @@
</span><span class="cx"> #endif
</span><span class="cx"> };
</span><span class="cx">
</span><ins>+static_assert(largeChunkMetadataSize == sizeof(LargeChunk), "'largeChunkMetadataSize' should be the same number as sizeof(LargeChunk) or our computation in Sizes.h for 'largeMax' is wrong");
+static_assert(largeChunkMetadataSize + largeMax <= largeChunkSize, "We will think we can accommodate larger objects than we can in reality");
+
</ins><span class="cx"> inline LargeChunk* LargeChunk::get(void* object)
</span><span class="cx"> {
</span><span class="cx"> BASSERT(!isSmallOrMedium(object));
</span></span></pre></div>
<a id="trunkSourcebmallocbmallocSizesh"></a>
<div class="modfile"><h4>Modified: trunk/Source/bmalloc/bmalloc/Sizes.h (196185 => 196186)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/bmalloc/bmalloc/Sizes.h 2016-02-05 21:22:39 UTC (rev 196185)
+++ trunk/Source/bmalloc/bmalloc/Sizes.h 2016-02-05 21:34:27 UTC (rev 196186)
</span><span class="lines">@@ -72,11 +72,16 @@
</span><span class="cx"> static const size_t mediumChunkMask = ~(mediumChunkSize - 1ul);
</span><span class="cx">
</span><span class="cx"> static const size_t largeChunkSize = superChunkSize / 2;
</span><ins>+#if BPLATFORM(IOS)
+ static const size_t largeChunkMetadataSize = 16 * kB;
+#else
+ static const size_t largeChunkMetadataSize = 4 * kB;
+#endif
</ins><span class="cx"> static const size_t largeChunkOffset = 0;
</span><span class="cx"> static const size_t largeChunkMask = ~(largeChunkSize - 1ul);
</span><span class="cx">
</span><span class="cx"> static const size_t largeAlignment = 64;
</span><del>- static const size_t largeMax = largeChunkSize * 99 / 100; // Plenty of room for metadata.
</del><ins>+ static const size_t largeMax = largeChunkSize - largeChunkMetadataSize;
</ins><span class="cx"> static const size_t largeMin = mediumMax;
</span><span class="cx">
</span><span class="cx"> static const size_t xLargeAlignment = vmPageSize;
</span></span></pre></div>
<a id="trunkSourcebmallocbmallocVMHeapcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/bmalloc/bmalloc/VMHeap.cpp (196185 => 196186)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/bmalloc/bmalloc/VMHeap.cpp 2016-02-05 21:22:39 UTC (rev 196185)
+++ trunk/Source/bmalloc/bmalloc/VMHeap.cpp 2016-02-05 21:34:27 UTC (rev 196186)
</span><span class="lines">@@ -53,7 +53,9 @@
</span><span class="cx"> m_mediumPages.push(it);
</span><span class="cx">
</span><span class="cx"> LargeChunk* largeChunk = superChunk->largeChunk();
</span><del>- m_largeObjects.insert(LargeObject(LargeObject::init(largeChunk).begin()));
</del><ins>+ LargeObject result(LargeObject::init(largeChunk).begin());
+ BASSERT(result.size() == largeMax);
+ m_largeObjects.insert(result);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> } // namespace bmalloc
</span></span></pre>
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