1 files changed, 23 insertions, 14 deletions

diff --git a/tensorflow/core/common_runtime/bfc_allocator.h b/tensorflow/core/common_runtime/bfc_allocator.h
index 52aedb1e9c..580e61e2ea 100644
--- a/tensorflow/core/common_runtime/bfc_allocator.h
+++ b/tensorflow/core/common_runtime/bfc_allocator.h
@@ -88,11 +88,20 @@ class BFCAllocator : public VisitableAllocator {
   static const int kInvalidBinNum = -1;
   static const int kNumBins = 21;
 
-  // Chunks point to memory.  Their prev/next pointers form a
-  // doubly-linked list of addresses sorted by base address that
-  // must be contiguous.  Chunks contain information about whether
-  // they are in use or whether they are free, and contain a pointer
-  // to the bin they are in.
+  // A Chunk points to a piece of memory that's either entirely free or entirely
+  // in use by one user memory allocation.
+  //
+  // An AllocationRegion's memory is split up into one or more disjoint Chunks,
+  // which together cover the whole region without gaps.  Chunks participate in
+  // a doubly-linked list, and the prev/next pointers point to the physically
+  // adjacent chunks.
+  //
+  // Since a chunk cannot be partially in use, we may need to split a free chunk
+  // in order to service a user allocation.  We always merge adjacent free
+  // chunks.
+  //
+  // Chunks contain information about whether they are in use or whether they
+  // are free, and contain a pointer to the bin they are in.
   struct Chunk {
     size_t size = 0;  // Full size of buffer.
 
@@ -177,8 +186,12 @@ class BFCAllocator : public VisitableAllocator {
   static const size_t kMinAllocationBits = 8;
   static const size_t kMinAllocationSize = 1 << kMinAllocationBits;
 
-  // AllocationRegion maps pointers to ChunkHandles for a single
-  // contiguous memory region.
+  // BFCAllocator allocates memory into a collection of disjoint
+  // AllocationRegions.  Each AllocationRegion corresponds to one call to
+  // SubAllocator::Alloc().
+  //
+  // An AllocationRegion contains one or more Chunks, covering all of its
+  // memory.  Its primary job is to map a pointers to ChunkHandles.
   //
   // This class is thread-compatible.
   class AllocationRegion {
@@ -191,18 +204,14 @@ class BFCAllocator : public VisitableAllocator {
       DCHECK_EQ(0, memory_size % kMinAllocationSize);
       const size_t n_handles =
           (memory_size + kMinAllocationSize - 1) / kMinAllocationSize;
-      handles_ = new ChunkHandle[n_handles];
+      handles_.reset(new ChunkHandle[n_handles]);
       for (size_t i = 0; i < n_handles; i++) {
         handles_[i] = kInvalidChunkHandle;
       }
     }
 
-    AllocationRegion() {}
-
-    ~AllocationRegion() { delete[] handles_; }
-
+    AllocationRegion() = default;
     AllocationRegion(AllocationRegion&& other) { Swap(other); }
-
     AllocationRegion& operator=(AllocationRegion&& other) {
       Swap(other);
       return *this;
@@ -241,7 +250,7 @@ class BFCAllocator : public VisitableAllocator {
     // Array of size "memory_size / kMinAllocationSize".  It is
     // indexed by (p-base) / kMinAllocationSize, contains ChunkHandle
     // for the memory allocation represented by "p"
-    ChunkHandle* handles_ = nullptr;
+    std::unique_ptr<ChunkHandle[]> handles_;
 
     TF_DISALLOW_COPY_AND_ASSIGN(AllocationRegion);
   };