PartitionAlloc: Distinguish OOMs where a lot of super pages are not committed

Source/wtf/PartitionAlloc.cpp

Index: Source/wtf/PartitionAlloc.cpp
diff --git a/Source/wtf/PartitionAlloc.cpp b/Source/wtf/PartitionAlloc.cpp
index ab14a4328f122cd7b2e7b56e31c6fc83aadc98c6..b65bf5b3a7eb0526ab43f6a9d42ca1e79329732c 100644
--- a/Source/wtf/PartitionAlloc.cpp
+++ b/Source/wtf/PartitionAlloc.cpp
@@ -296,8 +296,16 @@ bool partitionAllocGenericShutdown(PartitionRootGeneric* root)
     return noLeaks;
 }
 
-static NEVER_INLINE void partitionOutOfMemory()
+static NEVER_INLINE void partitionOutOfMemory(const PartitionRootBase* root)
 {
+    if ((uint64_t)root->totalSizeOfCommittedPages + 1000000000 < (uint64_t)root->totalSizeOfSuperPages) {

[kouhei (in TOK), 2014/10/29 09:34:32]

1000000000 should be named as "static const size_t kReasonableSizeOfUnusedPages"
if (r->totalSizeOfSuperPages - r->totalSizeOfCommittedPages >
kReasonableSizeOfUnusedPages)

[hiroshige, 2014/11/06 10:59:13]

Done.

+        // OOMs where a lot of super pages are allocated but not committed,
+        // probably due to http://crbug.com/421387.
+        // Crash at a special address (0x9b)
+        // to be easily distinguished on crash reports.
+        ((void(*)())0x0000009b)();
+    }
+    // Ordinary OOMs (where super pages are consumed and mostly committed).
     IMMEDIATE_CRASH();
 }
 
@@ -701,7 +709,7 @@ void* partitionAllocSlowPath(PartitionRootBase* root, int flags, size_t size, Pa
 partitionAllocSlowPathFailed:
     if (returnNull)
         return nullptr;
-    partitionOutOfMemory();
+    partitionOutOfMemory(root);
     return nullptr;
 }