Reland "[lldb] Increase the rate at which ConstString's memory allocator scales the...

The parent revision is now passing the sanitizer bots and landed as 46e5603c8a08de6c5983ed7eb4f12828bbfcbd78,
so this can now actually land.

diff --git a/lldb/source/Utility/ConstString.cpp b/lldb/source/Utility/ConstString.cpp
index 4e353df..356d211 100644 (file)
--- a/lldb/source/Utility/ConstString.cpp
+++ b/lldb/source/Utility/ConstString.cpp
@@ -29,9 +29,37 @@ using namespace lldb_private;
 
 class Pool {
 public:
+  /// The default BumpPtrAllocatorImpl slab size.
+  static const size_t AllocatorSlabSize = 4096;
+  static const size_t SizeThreshold = AllocatorSlabSize;
+  /// Every Pool has its own allocator which receives an equal share of
+  /// the ConstString allocations. This means that when allocating many
+  /// ConstStrings, every allocator sees only its small share of allocations and
+  /// assumes LLDB only allocated a small amount of memory so far. In reality
+  /// LLDB allocated a total memory that is N times as large as what the
+  /// allocator sees (where N is the number of string pools). This causes that
+  /// the BumpPtrAllocator continues a long time to allocate memory in small
+  /// chunks which only makes sense when allocating a small amount of memory
+  /// (which is true from the perspective of a single allocator). On some
+  /// systems doing all these small memory allocations causes LLDB to spend
+  /// a lot of time in malloc, so we need to force all these allocators to
+  /// behave like one allocator in terms of scaling their memory allocations
+  /// with increased demand. To do this we set the growth delay for each single
+  /// allocator to a rate so that our pool of allocators scales their memory
+  /// allocations similar to a single BumpPtrAllocatorImpl.
+  ///
+  /// Currently we have 256 string pools and the normal growth delay of the
+  /// BumpPtrAllocatorImpl is 128 (i.e., the memory allocation size increases
+  /// every 128 full chunks), so by changing the delay to 1 we get a
+  /// total growth delay in our allocator collection of 256/1 = 256. This is
+  /// still only half as fast as a normal allocator but we can't go any faster
+  /// without decreasing the number of string pools.
+  static const size_t AllocatorGrowthDelay = 1;
+  typedef llvm::BumpPtrAllocatorImpl<llvm::MallocAllocator, AllocatorSlabSize,
+                                     SizeThreshold, AllocatorGrowthDelay>
+      Allocator;
   typedef const char *StringPoolValueType;
-  typedef llvm::StringMap<StringPoolValueType, llvm::BumpPtrAllocator>
-      StringPool;
+  typedef llvm::StringMap<StringPoolValueType, Allocator> StringPool;
   typedef llvm::StringMapEntry<StringPoolValueType> StringPoolEntryType;
 
   static StringPoolEntryType &