diff --git a/crate/memory/src/lib.rs b/crate/memory/src/lib.rs
index ffdb24b..4f08587 100644
--- a/crate/memory/src/lib.rs
+++ b/crate/memory/src/lib.rs
@@ -4,4 +4,7 @@
 extern crate alloc;
 
 pub mod memory_set;
-pub mod swap;
\ No newline at end of file
+pub mod swap;
+pub mod page_table;
+
+type VirtAddr = usize;
\ No newline at end of file
diff --git a/crate/memory/src/swap/mock_page_table.rs b/crate/memory/src/page_table/mock_page_table.rs
similarity index 74%
rename from crate/memory/src/swap/mock_page_table.rs
rename to crate/memory/src/page_table/mock_page_table.rs
index b3f0088..b26e6c0 100644
--- a/crate/memory/src/swap/mock_page_table.rs
+++ b/crate/memory/src/page_table/mock_page_table.rs
@@ -2,36 +2,47 @@ use alloc::btree_set::BTreeSet;
 use super::*;
 
 pub struct MockPageTable {
-    mapped_set: BTreeSet<Addr>,
-    accessed_set: BTreeSet<Addr>,
-    dirty_set: BTreeSet<Addr>,
+    mapped_set: BTreeSet<VirtAddr>,
+    accessed_set: BTreeSet<VirtAddr>,
+    dirty_set: BTreeSet<VirtAddr>,
     page_fault_handler: PageFaultHandler,
     capacity: usize,
 }
 
-type PageFaultHandler = fn(&mut MockPageTable, Addr);
+type PageFaultHandler = fn(&mut MockPageTable, VirtAddr);
 
 impl PageTable for MockPageTable {
-    fn accessed(&self, addr: Addr) -> bool {
+    fn accessed(&self, addr: VirtAddr) -> bool {
         self.accessed_set.contains(&addr)
     }
-    fn dirty(&self, addr: Addr) -> bool {
+    fn dirty(&self, addr: VirtAddr) -> bool {
         self.dirty_set.contains(&addr)
     }
+    /// Map a page, return false if no more space
+    fn map(&mut self, addr: VirtAddr) -> bool {
+        if self.mapped_set.len() == self.capacity {
+            return false;
+        }
+        self.mapped_set.insert(addr);
+        true
+    }
+    fn unmap(&mut self, addr: VirtAddr) {
+        self.mapped_set.remove(&addr);
+    }
 }
 
 impl MockPageTable {
     pub fn new(capacity: usize, page_fault_handler: PageFaultHandler) -> Self {
         MockPageTable {
-            mapped_set: BTreeSet::<Addr>::new(),
-            accessed_set: BTreeSet::<Addr>::new(),
-            dirty_set: BTreeSet::<Addr>::new(),
+            mapped_set: BTreeSet::<VirtAddr>::new(),
+            accessed_set: BTreeSet::<VirtAddr>::new(),
+            dirty_set: BTreeSet::<VirtAddr>::new(),
             page_fault_handler,
             capacity,
         }
     }
     /// Read memory, mark accessed, trigger page fault if not present
-    pub fn read(&mut self, addr: Addr) {
+    pub fn read(&mut self, addr: VirtAddr) {
         while !self.mapped_set.contains(&addr) {
             (self.page_fault_handler)(self, addr);
         }
@@ -39,25 +50,13 @@ impl MockPageTable {
 
     }
     /// Write memory, mark accessed and dirty, trigger page fault if not present
-    pub fn write(&mut self, addr: Addr) {
+    pub fn write(&mut self, addr: VirtAddr) {
         while !self.mapped_set.contains(&addr) {
             (self.page_fault_handler)(self, addr);
         }
         self.accessed_set.insert(addr);
         self.dirty_set.insert(addr);
     }
-    /// Map a page, return false if no more space
-    pub fn map(&mut self, addr: Addr) -> bool {
-        if self.mapped_set.len() == self.capacity {
-            return false;
-        }
-        self.mapped_set.insert(addr);
-        true
-    }
-    /// Unmap a page
-    pub fn unmap(&mut self, addr: Addr) {
-        self.mapped_set.remove(&addr);
-    }
 }
 
 #[cfg(test)]
@@ -72,7 +71,7 @@ mod test {
 
     #[test]
     fn test() {
-        fn page_fault_handler(pt: &mut MockPageTable, addr: Addr) {
+        fn page_fault_handler(pt: &mut MockPageTable, addr: VirtAddr) {
             unsafe{ PGFAULT_COUNT += 1; }
             pt.map(addr);
         }
diff --git a/crate/memory/src/page_table/mod.rs b/crate/memory/src/page_table/mod.rs
new file mode 100644
index 0000000..245311a
--- /dev/null
+++ b/crate/memory/src/page_table/mod.rs
@@ -0,0 +1,10 @@
+use super::*;
+
+pub mod mock_page_table;
+
+pub trait PageTable {
+    fn accessed(&self, addr: VirtAddr) -> bool;
+    fn dirty(&self, addr: VirtAddr) -> bool;
+    fn map(&mut self, addr: VirtAddr) -> bool;
+    fn unmap(&mut self, addr: VirtAddr);
+}
\ No newline at end of file
diff --git a/crate/memory/src/swap/fifo.rs b/crate/memory/src/swap/fifo.rs
index 4a006ee..fd7c912 100644
--- a/crate/memory/src/swap/fifo.rs
+++ b/crate/memory/src/swap/fifo.rs
@@ -3,14 +3,14 @@ use super::*;
 
 struct FifoSwapManager<T: 'static + PageTable> {
     page_table: &'static T,
-    deque: VecDeque<Addr>,
+    deque: VecDeque<VirtAddr>,
 }
 
 impl<T: 'static + PageTable> SwapManager<T> for FifoSwapManager<T> {
     fn new(page_table: &'static T) -> Self {
         FifoSwapManager {
             page_table,
-            deque: VecDeque::<Addr>::new()
+            deque: VecDeque::<VirtAddr>::new()
         }
     }
 
@@ -29,7 +29,7 @@ impl<T: 'static + PageTable> SwapManager<T> for FifoSwapManager<T> {
         self.deque.remove(id);
     }
 
-    fn pop(&mut self) -> Option<Addr> {
+    fn pop(&mut self) -> Option<VirtAddr> {
         self.deque.pop_front()
     }
 }
@@ -37,7 +37,7 @@ impl<T: 'static + PageTable> SwapManager<T> for FifoSwapManager<T> {
 #[cfg(test)]
 mod test {
     use super::*;
-    use super::mock_page_table::MockPageTable;
+    use page_table::mock_page_table::MockPageTable;
 
     enum MemOp {
         R(usize), W(usize)
@@ -52,7 +52,7 @@ mod test {
     static mut PAGE: *mut MockPageTable = 0 as *mut _;
     static mut FIFO: *mut FifoSwapManager<MockPageTable> = 0 as *mut _;
 
-    fn page_fault_handler(pt: &mut MockPageTable, addr: Addr) {
+    fn page_fault_handler(pt: &mut MockPageTable, addr: VirtAddr) {
         unsafe{ PGFAULT_COUNT += 1; }
         let fifo = unsafe{ &mut *FIFO };
         if !pt.map(addr) {  // is full?
diff --git a/crate/memory/src/swap/mod.rs b/crate/memory/src/swap/mod.rs
index 214779c..6d1c350 100644
--- a/crate/memory/src/swap/mod.rs
+++ b/crate/memory/src/swap/mod.rs
@@ -1,25 +1,20 @@
+use super::*;
+use super::page_table::PageTable;
+
 pub mod fifo;
-mod mock_page_table;
 mod mock_swapper;
 
-type Addr = usize;
-
 trait SwapManager<T: PageTable> {
     /// Create and initialize for the swap manager
     fn new(page_table: &'static T) -> Self;
     /// Called when tick interrupt occured
     fn tick(&mut self);
     /// Called when map a swappable page into the memory
-    fn push(&mut self, addr: Addr);
+    fn push(&mut self, addr: VirtAddr);
     /// Called to delete the addr entry from the swap manager
-    fn remove(&mut self, addr: Addr);
+    fn remove(&mut self, addr: VirtAddr);
     /// Try to swap out a page, return then victim
-    fn pop(&mut self) -> Option<Addr>;
-}
-
-trait PageTable {
-    fn accessed(&self, addr: Addr) -> bool;
-    fn dirty(&self, addr: Addr) -> bool;
+    fn pop(&mut self) -> Option<VirtAddr>;
 }
 
 trait Swapper {