diff --git a/code/lab2/kern/mm/memlayout.h b/code/lab2/kern/mm/memlayout.h
index 12af91c..1e58466 100644
--- a/code/lab2/kern/mm/memlayout.h
+++ b/code/lab2/kern/mm/memlayout.h
@@ -104,8 +104,8 @@ struct Page {
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))
diff --git a/code/lab3/kern/mm/memlayout.h b/code/lab3/kern/mm/memlayout.h
index f0c6816..33b4ea4 100644
--- a/code/lab3/kern/mm/memlayout.h
+++ b/code/lab3/kern/mm/memlayout.h
@@ -107,8 +107,8 @@ struct Page {
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))
diff --git a/code/lab4/kern/mm/memlayout.h b/code/lab4/kern/mm/memlayout.h
index b6b4094..af1fcb9 100644
--- a/code/lab4/kern/mm/memlayout.h
+++ b/code/lab4/kern/mm/memlayout.h
@@ -100,16 +100,15 @@ struct e820map {
 struct Page {
     int ref;                        // page frame's reference counter
     uint32_t flags;                 // array of flags that describe the status of the page frame
-    unsigned int property;          // used in buddy system, stores the order (the X in 2^X) of the continuous memory block
-    int zone_num;                   // used in buddy system, the No. of zone which the page belongs to
+    unsigned int property;          // the num of free block, used in first fit pm manager
     list_entry_t page_link;         // free list link
     list_entry_t pra_page_link;     // used for pra (page replace algorithm)
     uintptr_t pra_vaddr;            // used for pra (page replace algorithm)
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))
diff --git a/code/lab5/kern/mm/memlayout.h b/code/lab5/kern/mm/memlayout.h
index 825dd66..aa6a4ce 100644
--- a/code/lab5/kern/mm/memlayout.h
+++ b/code/lab5/kern/mm/memlayout.h
@@ -129,16 +129,15 @@ struct e820map {
 struct Page {
     int ref;                        // page frame's reference counter
     uint32_t flags;                 // array of flags that describe the status of the page frame
-    unsigned int property;          // used in buddy system, stores the order (the X in 2^X) of the continuous memory block
-    int zone_num;                   // used in buddy system, the No. of zone which the page belongs to
+    unsigned int property;          // the num of free block, used in first fit pm manager
     list_entry_t page_link;         // free list link
     list_entry_t pra_page_link;     // used for pra (page replace algorithm)
     uintptr_t pra_vaddr;            // used for pra (page replace algorithm)
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))
diff --git a/code/lab6/kern/mm/memlayout.h b/code/lab6/kern/mm/memlayout.h
index 825dd66..aa6a4ce 100644
--- a/code/lab6/kern/mm/memlayout.h
+++ b/code/lab6/kern/mm/memlayout.h
@@ -129,16 +129,15 @@ struct e820map {
 struct Page {
     int ref;                        // page frame's reference counter
     uint32_t flags;                 // array of flags that describe the status of the page frame
-    unsigned int property;          // used in buddy system, stores the order (the X in 2^X) of the continuous memory block
-    int zone_num;                   // used in buddy system, the No. of zone which the page belongs to
+    unsigned int property;          // the num of free block, used in first fit pm manager
     list_entry_t page_link;         // free list link
     list_entry_t pra_page_link;     // used for pra (page replace algorithm)
     uintptr_t pra_vaddr;            // used for pra (page replace algorithm)
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))
diff --git a/code/lab7/kern/mm/memlayout.h b/code/lab7/kern/mm/memlayout.h
index 825dd66..aa6a4ce 100644
--- a/code/lab7/kern/mm/memlayout.h
+++ b/code/lab7/kern/mm/memlayout.h
@@ -129,16 +129,15 @@ struct e820map {
 struct Page {
     int ref;                        // page frame's reference counter
     uint32_t flags;                 // array of flags that describe the status of the page frame
-    unsigned int property;          // used in buddy system, stores the order (the X in 2^X) of the continuous memory block
-    int zone_num;                   // used in buddy system, the No. of zone which the page belongs to
+    unsigned int property;          // the num of free block, used in first fit pm manager
     list_entry_t page_link;         // free list link
     list_entry_t pra_page_link;     // used for pra (page replace algorithm)
     uintptr_t pra_vaddr;            // used for pra (page replace algorithm)
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))
diff --git a/code/lab8/kern/mm/memlayout.h b/code/lab8/kern/mm/memlayout.h
index 825dd66..aa6a4ce 100644
--- a/code/lab8/kern/mm/memlayout.h
+++ b/code/lab8/kern/mm/memlayout.h
@@ -129,16 +129,15 @@ struct e820map {
 struct Page {
     int ref;                        // page frame's reference counter
     uint32_t flags;                 // array of flags that describe the status of the page frame
-    unsigned int property;          // used in buddy system, stores the order (the X in 2^X) of the continuous memory block
-    int zone_num;                   // used in buddy system, the No. of zone which the page belongs to
+    unsigned int property;          // the num of free block, used in first fit pm manager
     list_entry_t page_link;         // free list link
     list_entry_t pra_page_link;     // used for pra (page replace algorithm)
     uintptr_t pra_vaddr;            // used for pra (page replace algorithm)
 };
 
 /* Flags describing the status of a page frame */
-#define PG_reserved                 0       // the page descriptor is reserved for kernel or unusable
-#define PG_property                 1       // the member 'property' is valid
+#define PG_reserved                 0       // if this bit=1: the Page is reserved for kernel, cannot be used in alloc/free_pages; otherwise, this bit=0 
+#define PG_property                 1       // if this bit=1: the Page is the head page of a free memory block(contains some continuous_addrress pages), and can be used in alloc_pages; if this bit=0: if the Page is the the head page of a free memory block, then this Page and the memory block is alloced. Or this Page isn't the head page.
 
 #define SetPageReserved(page)       set_bit(PG_reserved, &((page)->flags))
 #define ClearPageReserved(page)     clear_bit(PG_reserved, &((page)->flags))