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

Source/wtf/PartitionAlloc.h

Index: Source/wtf/PartitionAlloc.h
diff --git a/Source/wtf/PartitionAlloc.h b/Source/wtf/PartitionAlloc.h
index 51430004a09483d44187abd040cf4249159dfabb..7d9d9e4f869373e1f3d5ca798bf2ab5208842f49 100644
--- a/Source/wtf/PartitionAlloc.h
+++ b/Source/wtf/PartitionAlloc.h
@@ -184,6 +184,10 @@ static const size_t kBitsPerSizet = sizeof(void*) * CHAR_BIT;
 // Constants for the memory reclaim logic.
 static const size_t kMaxFreeableSpans = 16;
 
+// If the total size of allocated but not committed pages exceeds this value,

[Tom Sepez, 2014/11/06 17:32:51]

nit: size in bytes?  pages? 

[Chris Evans, 2014/11/06 20:43:22]

Nit: this comment doesn't really explain why we'd want to do this. Maybe explain
"this is to try and distinguish "out of address space" from "out of physical
memory" ?

[hiroshige, 2014/11/07 08:57:00]

In bytes. Add it to the comment.

[hiroshige, 2014/11/07 08:57:00]

Done.

[hiroshige, 2014/11/07 08:57:00]

Done.

+// special crash stack trace is generated at |partitionOutOfMemory|.

[Chris Evans, 2014/11/06 20:43:22]

Nit: "a special"?

[hiroshige, 2014/11/07 08:57:00]

Done.

+static const size_t kReasonableSizeOfUnusedPages = 1000000000;

[Chris Evans, 2014/11/06 20:43:22]

Nit: this looks to be about 1GB. Maybe formulate it as 1024 * 1024 * 1024 for
easy engineer readability?

[hiroshige, 2014/11/07 08:57:00]

Done.

+
 #if ENABLE(ASSERT)
 // These two byte values match tcmalloc.
 static const unsigned char kUninitializedByte = 0xAB;