diff --git a/src/share/allocator/ob_fifo_arena.cpp b/src/share/allocator/ob_fifo_arena.cpp
index 49896b6895..54cef08a0e 100644
--- a/src/share/allocator/ob_fifo_arena.cpp
+++ b/src/share/allocator/ob_fifo_arena.cpp
@@ -142,7 +142,7 @@ void ObFifoArena::shrink_cached_page(int64_t nway)
         if (NULL != ref) {
           // There may be concurrent removal, no need to pay attention to the return value
           UNUSED(ATOMIC_BCAS(paddr, page, NULL));
-          IGNORE_RETURN ATOMIC_FAA(&retired_, page->hold());
+          IGNORE_RETURN ATOMIC_FAA(&retired_, page->get_actual_hold_size());
           release_ref(ref);
         }
       }
@@ -169,7 +169,7 @@ void* ObFifoArena::alloc(int64_t adv_idx, Handle& handle, int64_t size)
       ret = OB_ALLOCATE_MEMORY_FAILED;
     } else {
       bool need_switch = false;
-      handle.add_allocated(page->hold());
+      handle.add_allocated(page->get_actual_hold_size());
       ptr = handle.ref_and_alloc(way_id, need_switch, page, size);
       page->frozen();
       retire_page(way_id, handle, page);
@@ -200,7 +200,7 @@ void* ObFifoArena::alloc(int64_t adv_idx, Handle& handle, int64_t size)
           UNUSED(ATOMIC_BCAS(paddr, page, NULL));
           ret = OB_ALLOCATE_MEMORY_FAILED;
         } else if (ATOMIC_BCAS(paddr, page, new_page)) {
-          handle.add_allocated(new_page->hold());
+          handle.add_allocated(new_page->get_actual_hold_size());
         } else {
           destroy_page(new_page);
         }
@@ -239,8 +239,8 @@ ObFifoArena::Page* ObFifoArena::alloc_page(int64_t size)
 {
   Page* page = (Page*)allocator_->alloc(size, attr_);
   if (NULL != page) {
-    ATOMIC_FAA(&allocated_, size);
-    ATOMIC_FAA(&total_hold_, size);
+    ATOMIC_FAA(&allocated_, page->get_actual_hold_size());
+    ATOMIC_FAA(&total_hold_, page->get_actual_hold_size());
     ATOMIC_AAF(&hold_, page->get_actual_hold_size());
     page->set(size);
   }
@@ -250,8 +250,8 @@ ObFifoArena::Page* ObFifoArena::alloc_page(int64_t size)
 void ObFifoArena::free_page(Page* page)
 {
   if (NULL != page && NULL != allocator_) {
-    ATOMIC_FAA(&reclaimed_, page->hold());
-    ATOMIC_FAA(&total_hold_, -page->hold());
+    ATOMIC_FAA(&reclaimed_, page->get_actual_hold_size());
+    ATOMIC_FAA(&total_hold_, -page->get_actual_hold_size());
     ATOMIC_FAA(&hold_, -page->get_actual_hold_size());
     allocator_->free(page);
   }
@@ -260,7 +260,7 @@ void ObFifoArena::free_page(Page* page)
 void ObFifoArena::retire_page(int64_t idx, Handle& handle, Page* page)
 {
   if (NULL != page) {
-    ATOMIC_FAA(&retired_, page->hold());
+    ATOMIC_FAA(&retired_, page->get_actual_hold_size());
     handle.add_ref(idx, &page->self_ref_);
   }
 }
@@ -268,8 +268,9 @@ void ObFifoArena::retire_page(int64_t idx, Handle& handle, Page* page)
 void ObFifoArena::destroy_page(Page* page)
 {
   if (NULL != page && NULL != allocator_) {
-    ATOMIC_FAA(&allocated_, -page->hold());
-    ATOMIC_FAA(&total_hold_, -page->hold());
+    ATOMIC_FAA(&allocated_, -page->get_actual_hold_size());
+    ATOMIC_FAA(&total_hold_, -page->get_actual_hold_size());
+    ATOMIC_FAA(&hold_, -page->get_actual_hold_size());
     allocator_->free(page);
   }
 }
diff --git a/src/share/allocator/ob_fifo_arena.h b/src/share/allocator/ob_fifo_arena.h
index 207bc0dea7..5e8304c568 100644
--- a/src/share/allocator/ob_fifo_arena.h
+++ b/src/share/allocator/ob_fifo_arena.h
@@ -44,7 +44,7 @@ public:
     }
     Ref* next_;
     Page* page_;
-    int64_t allocated_;
+    int64_t allocated_; // the allocated bytes from page
   };
 
   struct Page
@@ -81,9 +81,9 @@ public:
       return ref;
     }
     int64_t get_actual_hold_size();
-    Ref self_ref_;
-    int64_t limit_;
-    int64_t pos_;
+    Ref self_ref_;  // record the allocated bytes from page, include self_ref_ itself
+    int64_t limit_; // the max bytes of a page that can be used
+    int64_t pos_;   // the position after which can be allocated
     int64_t ref_;
     char buf_[0];
   };
@@ -141,7 +141,8 @@ public:
     TO_STRING_KV(K_(allocated));
     int64_t lock_;
     Ref* ref_[MAX_NWAY];
-    int64_t allocated_;
+    int64_t allocated_;  // record all the memory hold by pages, include the size of page structure, AObject and so on.
+                         // only increase while a page is created.
   };
 
 public:
@@ -233,10 +234,14 @@ private:
   lib::ObMemAttr attr_;
   lib::ObIAllocator *allocator_;
   int64_t nway_;
-  int64_t allocated_;
-  int64_t reclaimed_;
-  int64_t hold_;//for single tenant
-  int64_t retired_;
+  int64_t allocated_; // record all the memory hold by pages in history.
+                      // increase while a page created and decrease only if a failed page destroyed.
+  int64_t reclaimed_; // record all the memory reclaimed by pages in history.
+                      // increase while a page freed.
+  int64_t hold_;      // record all the memory hold by pages current.
+                      // increase while a page created and decrease while a page freed or destroyed.
+                      // (may be: hold_ = allocated_ - reclaimed_)
+  int64_t retired_;   // record all the memory hold by not active pages in history.
 
   int64_t max_seq_;
   int64_t clock_;