diff --git a/libhidlmemory/include/hidlmemory/mapping.h b/libhidlmemory/include/hidlmemory/mapping.h
index 5e1dab3..e15eb80 100644
--- a/libhidlmemory/include/hidlmemory/mapping.h
+++ b/libhidlmemory/include/hidlmemory/mapping.h
@@ -22,6 +22,9 @@
 /**
  * Returns the IMemory instance corresponding to a hidl_memory object.
  * If the shared memory cannot be fetched, this returns nullptr.
+ *
+ * Note, this method call is relatively expensive and does not cache conversions.
+ * It should only be done when initializing a buffer and not on every buffer read.
  */
 sp<android::hidl::memory::V1_0::IMemory> mapMemory(const hidl_memory &memory);