diff --git a/arch/xtensa/src/esp32/esp32_allocateheap.c b/arch/xtensa/src/esp32/esp32_allocateheap.c
index a2f28d45daf..757ef8e2fde 100644
--- a/arch/xtensa/src/esp32/esp32_allocateheap.c
+++ b/arch/xtensa/src/esp32/esp32_allocateheap.c
@@ -53,6 +53,35 @@
  * Pre-processor Definitions
  ****************************************************************************/
 
+/* The heap overview:
+ *
+ * CONFIG_HEAP2_BASE                         eg. 3f80 0000
+ *     :
+ *     : g_mmheap region3 (CONFIG_ESP32_SPIRAM)
+ *     :
+ * CONFIG_HEAP2_BASE + CONFIG_HEAP2_SIZE     eg. 3fc0 0000
+ *
+ * _sheap                                    eg. 3ffc 8c6c
+ *     :
+ *     : g_iheap (CONFIG_XTENSA_USE_SEPARATE_IMEM)
+ *     :
+ * _sheap + CONFIG_XTENSA_IMEM_REGION_SIZE   eg. 3ffd ebfc
+ *     :
+ *     : g_mmheap region1
+ *     :
+ * HEAP_REGION1_END                              3ffd fff0
+ *     :
+ *     : ROM data
+ *     :
+ * HEAP_REGION2_START                            3ffe 1330 or 3ffe 7e40
+ *     :
+ *     : g_mmheap region2
+ *     :
+ *     : about 123KB
+ *     :
+ * _eheap                                        4000 0000
+ */
+
 /* Region 1 of the heap is the area from the end of the .data section to the
  * begining of the ROM data.  The start address is defined from the linker
  * script as "_sheap".  Then end is defined here, as follows: