update comments

src/storage/cpu_device_storage.h

@@ -40,13 +40,12 @@ class CPUDeviceStorage {
  public:
   /*!
    * \brief Aligned allocation on CPU.
-   * \param size Size to allocate.
-   * \return Pointer to the storage.
+   * \param handle Handle struct.
    */
   inline static void* Alloc(Storage::Handle* handle);
   /*!
    * \brief Deallocation.
-   * \param ptr Pointer to deallocate.
+   * \param handle Handle struct.
    */
   inline static void Free(Storage::Handle handle);
 

src/storage/gpu_device_storage.h

@@ -43,13 +43,12 @@ class GPUDeviceStorage {
  public:
   /*!
    * \brief Allocation.
-   * \param size Size to allocate.
-   * \return Pointer to the storage.
+   * \param handle Handle struct.
    */
   inline static void* Alloc(Storage::Handle* handle);
   /*!
    * \brief Deallocation.
-   * \param ptr Pointer to deallocate.
+   * \param handle Handle struct.
    */
   inline static void Free(Storage::Handle handle);
 };  // class GPUDeviceStorage

src/storage/pinned_memory_storage.h

@@ -38,14 +38,13 @@ class PinnedMemoryStorage {
  public:
   /*!
    * \brief Allocation.
-   * \param size Size to allocate.
-   * \return Pointer to the storage.
+   * \param handle Handle struct.
    */
   inline static void* Alloc(Storage::Handle* handle);
 
   /*!
    * \brief Deallocation.
-   * \param ptr Pointer to deallocate.
+   * \param handle Handle struct.
    */
   inline static void Free(Storage::Handle handle);
 };

src/storage/storage.cc

@@ -127,7 +127,8 @@ void StorageImpl::Alloc(Storage::Handle* handle) {
 }
 
 void StorageImpl::Free(Storage::Handle handle) {
-  // Do nothing if dtpr is nullptr.
+  // Do nothing if dtpr is nullptr because the handle may have already
+  // been freed or have not been allocated memory yet.
   if (handle.dptr == nullptr) return;
 
   const Context &ctx = handle.ctx;
@@ -143,7 +144,8 @@ void StorageImpl::Free(Storage::Handle handle) {
 }
 
 void StorageImpl::DirectFree(Storage::Handle handle) {
-  // Do nothing if dtpr is nullptr.
+  // Do nothing if dtpr is nullptr because the handle may have already
+  // been freed or have not been allocated memory yet.
   if (handle.dptr == nullptr) return;
 
   const Context &ctx = handle.ctx;

src/storage/storage_manager.h

@@ -39,20 +39,17 @@ class StorageManager {
  public:
   /*!
    * \brief Allocation.
-   * \param size Size to allocate.
-   * \return Pointer to the storage.
+   * \param handle Handle struct.
    */
   virtual void Alloc(Storage::Handle* handle) = 0;
   /*!
    * \brief Deallocation.
-   * \param ptr Pointer to deallocate.
-   * \param size Size of the storage.
+   * \param handle Handle struct.
    */
   virtual void Free(Storage::Handle handle) = 0;
   /*!
-   * \brief Direct de-allocation.
-   * \param ptr Pointer to deallocate.
-   * \param size Size of the storage.
+   * \brief Direct deallocation.
+   * \param handle Handle struct.
    */
   virtual void DirectFree(Storage::Handle handle) = 0;
   /*!