diff --git a/src/arch/x86_64/interrupt/template.rs b/src/arch/x86_64/interrupt/template.rs
index 80675273..fcafe6ea 100644
--- a/src/arch/x86_64/interrupt/template.rs
+++ b/src/arch/x86_64/interrupt/template.rs
@@ -151,7 +151,6 @@ macro_rules! iret {
 }
 
 /// Create an interrupt function that can safely run rust code
-#[macro_export]
 macro_rules! interrupt {
     ($name:ident, $func:block) => {
         #[naked]
@@ -198,7 +197,6 @@ impl InterruptStack {
     }
 }
 
-#[macro_export]
 macro_rules! interrupt_stack {
     ($name:ident, $stack: ident, $func:block) => {
         #[naked]
@@ -251,7 +249,6 @@ impl InterruptErrorStack {
     }
 }
 
-#[macro_export]
 macro_rules! interrupt_error {
     ($name:ident, $stack:ident, $func:block) => {
         #[naked]
@@ -317,7 +314,6 @@ impl Debug for InterruptStackP {
     }
 }
 
-#[macro_export]
 macro_rules! interrupt_switch {
     ($name:ident, $rsp: ident, $func:block) => {
         #[naked]
@@ -358,7 +354,6 @@ macro_rules! interrupt_switch {
     };
 }
 
-#[macro_export]
 macro_rules! interrupt_stack_p {
     ($name:ident, $stack: ident, $func:block) => {
         #[naked]
@@ -415,7 +410,6 @@ impl InterruptErrorStackP {
     }
 }
 
-#[macro_export]
 macro_rules! interrupt_error_p {
     ($name:ident, $stack:ident, $func:block) => {
         #[naked]
diff --git a/src/arch/x86_64/paging/mapper.rs b/src/arch/x86_64/paging/mapper.rs
index 69bdae4b..a8a9cf53 100644
--- a/src/arch/x86_64/paging/mapper.rs
+++ b/src/arch/x86_64/paging/mapper.rs
@@ -8,7 +8,7 @@ pub struct Mapper {
 }
 
 impl Mapper {
-    pub unsafe fn new() -> Mapper {
+    pub const unsafe fn new() -> Mapper {
         Mapper {
             p4: Unique::new_unchecked(table::P4),
         }
diff --git a/src/arch/x86_64/paging/mod.rs b/src/arch/x86_64/paging/mod.rs
index 8dfe2d7e..841ad7d3 100644
--- a/src/arch/x86_64/paging/mod.rs
+++ b/src/arch/x86_64/paging/mod.rs
@@ -105,7 +105,7 @@ impl DerefMut for ActivePageTable {
 }
 
 impl ActivePageTable {
-    pub unsafe fn new() -> ActivePageTable {
+    pub const unsafe fn new() -> ActivePageTable {
         ActivePageTable {
             mapper: Mapper::new(),
         }
diff --git a/src/lib.rs b/src/lib.rs
index 85c60cab..0a40bb74 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -50,7 +50,7 @@ mod syscall;
 #[path = "arch/x86_64/mod.rs"]
 mod arch;
 
-// The entry point of Rust kernel
+/// The entry point of Rust kernel
 #[no_mangle]
 pub extern "C" fn rust_main(multiboot_information_address: usize) -> ! {
     arch::cpu::init();
@@ -61,11 +61,7 @@ pub extern "C" fn rust_main(multiboot_information_address: usize) -> ! {
     let boot_info = unsafe { multiboot2::load(multiboot_information_address) };
 
     // set up guard page and map the heap pages
-    let mut memory_controller = memory::init(boot_info);    
-    unsafe {
-        use consts::{KERNEL_HEAP_OFFSET, KERNEL_HEAP_SIZE};
-        HEAP_ALLOCATOR.lock().init(KERNEL_HEAP_OFFSET, KERNEL_HEAP_SIZE);
-    }
+    let mut memory_controller = memory::init(boot_info);
 
     arch::gdt::init();
     arch::idt::init();
@@ -109,6 +105,7 @@ pub extern "C" fn rust_main(multiboot_information_address: usize) -> ! {
     unreachable!();
 }
 
+/// The entry point for another processors
 #[no_mangle]
 pub extern "C" fn other_main() -> ! {
     arch::cpu::init();
@@ -124,6 +121,11 @@ pub extern "C" fn other_main() -> ! {
 
 use linked_list_allocator::LockedHeap;
 
+/// Global heap allocator
+///
+/// Available after `memory::init()`.
+///
+/// It should be defined in memory mod, but in Rust `global_allocator` must be in root mod.
 #[global_allocator]
 static HEAP_ALLOCATOR: LockedHeap = LockedHeap::empty();
 
diff --git a/src/memory/memory_set.rs b/src/memory/memory_set.rs
index a6e510b4..65ef6fed 100644
--- a/src/memory/memory_set.rs
+++ b/src/memory/memory_set.rs
@@ -4,14 +4,13 @@ use core::fmt::{Debug, Formatter, Error};
 
 /// 一片连续内存空间，有相同的访问权限
 /// 对应ucore中 `vma_struct`
-#[derive(Debug, Eq, PartialEq)]
+#[derive(Debug, Eq, PartialEq, Copy, Clone)]
 pub struct MemoryArea {
     start_addr: VirtAddr,
     end_addr: VirtAddr,
     phys_start_addr: Option<PhysAddr>,
     flags: u64,
     name: &'static str,
-    mapped: bool,
 }
 
 impl MemoryArea {
@@ -23,7 +22,6 @@ impl MemoryArea {
             phys_start_addr: None,
             flags: flags.bits(),
             name,
-            mapped: false,
         }
     }
     pub fn new_identity(start_addr: VirtAddr, end_addr: VirtAddr, flags: EntryFlags, name: &'static str) -> Self {
@@ -34,7 +32,6 @@ impl MemoryArea {
             phys_start_addr: Some(PhysAddr(start_addr as u64)),
             flags: flags.bits(),
             name,
-            mapped: false,
         }
     }
     pub fn new_kernel(start_addr: VirtAddr, end_addr: VirtAddr, flags: EntryFlags, name: &'static str) -> Self {
@@ -45,7 +42,6 @@ impl MemoryArea {
             phys_start_addr: Some(PhysAddr::from_kernel_virtual(start_addr)),
             flags: flags.bits(),
             name,
-            mapped: false,
         }
     }
     pub fn contains(&self, addr: VirtAddr) -> bool {
@@ -94,9 +90,6 @@ impl MemorySet {
     }
     pub fn map(&mut self, pt: &mut Mapper) {
         for area in self.areas.iter_mut() {
-            if area.mapped {
-                continue
-            }
             match area.phys_start_addr {
                 Some(phys_start) => {
                     for page in Page::range_of(area.start_addr, area.end_addr) {
@@ -110,18 +103,13 @@ impl MemorySet {
                     }
                 },
             }
-            area.mapped = true;
         }
     }
     pub fn unmap(&mut self, pt: &mut Mapper) {
         for area in self.areas.iter_mut() {
-            if !area.mapped {
-                continue
-            }
             for page in Page::range_of(area.start_addr, area.end_addr) {
                 pt.unmap(page);
             }
-            area.mapped = false;
         }
     }
 }
diff --git a/src/memory/mod.rs b/src/memory/mod.rs
index 3770e7df..32da9d49 100644
--- a/src/memory/mod.rs
+++ b/src/memory/mod.rs
@@ -9,6 +9,7 @@ use multiboot2::BootInformation;
 use consts::KERNEL_OFFSET;
 use arch::paging;
 use spin::Mutex;
+use super::HEAP_ALLOCATOR;
 
 mod memory_set;
 mod area_frame_allocator;
@@ -17,6 +18,8 @@ mod stack_allocator;
 mod address;
 mod frame;
 
+pub static ACITVE_PAGETABLE: Mutex<ActivePageTable> = Mutex::new(unsafe { ActivePageTable::new() });
+
 pub static FRAME_ALLOCATOR: Mutex<Option<AreaFrameAllocator>> = Mutex::new(None);
 
 pub fn alloc_frame() -> Frame {
@@ -47,11 +50,13 @@ pub fn init(boot_info: BootInformation) -> MemoryController {
         memory_map_tag.memory_areas()
     ));
 
-    let (mut active_table, kernel_stack) = remap_the_kernel(boot_info);
+    let kernel_stack = remap_the_kernel(boot_info);
 
     use self::paging::Page;
     use consts::{KERNEL_HEAP_OFFSET, KERNEL_HEAP_SIZE};
 
+    unsafe { HEAP_ALLOCATOR.lock().init(KERNEL_HEAP_OFFSET, KERNEL_HEAP_SIZE); }
+
     let stack_allocator = {
         let stack_alloc_range = Page::range_of(KERNEL_HEAP_OFFSET + KERNEL_HEAP_SIZE,
                                                KERNEL_HEAP_OFFSET + KERNEL_HEAP_SIZE + 0x100000);
@@ -60,14 +65,14 @@ pub fn init(boot_info: BootInformation) -> MemoryController {
     
     MemoryController {
         kernel_stack: Some(kernel_stack),
-        active_table,
+        active_table: unsafe { ActivePageTable::new() },
         stack_allocator,
     }
 }
 
-pub fn remap_the_kernel(boot_info: BootInformation) -> (ActivePageTable, Stack)
+pub fn remap_the_kernel(boot_info: BootInformation) -> Stack
 {
-    let mut active_table = unsafe { ActivePageTable::new() };
+    let mut active_table = ACITVE_PAGETABLE.lock();
     let mut memory_set = MemorySet::from(boot_info.elf_sections_tag().unwrap());
 
     use consts::{KERNEL_HEAP_OFFSET, KERNEL_HEAP_SIZE};
@@ -90,7 +95,7 @@ pub fn remap_the_kernel(boot_info: BootInformation) -> (ActivePageTable, Stack)
     let kernel_stack = Stack::new(stack_bottom + 8 * PAGE_SIZE, stack_bottom + 1 * PAGE_SIZE);
     println!("guard page at {:#x}", stack_bottom_page.start_address());
 
-    (active_table, kernel_stack)
+    kernel_stack
 }
 
 use multiboot2::{ElfSectionsTag, ElfSection, ElfSectionFlags};
diff --git a/src/process/mod.rs b/src/process/mod.rs
index 75e88675..96a2ef0c 100644
--- a/src/process/mod.rs
+++ b/src/process/mod.rs
@@ -1,5 +1,6 @@
 use memory::MemoryController;
 use spin::{Once, Mutex};
+use core::slice;
 
 use self::process::*;
 use self::processor::*;
@@ -38,7 +39,7 @@ extern {
 
 pub fn init(mc: &mut MemoryController) {
     PROCESSOR.call_once(|| {Mutex::new({
-        let mut processor = Processor::new(mc);
+        let mut processor = Processor::new();
         let initproc = Process::new_init(mc);
         let idleproc = Process::new("idle", idle_thread, mc);
         #[cfg(feature = "link_user_program")]
diff --git a/src/process/process.rs b/src/process/process.rs
index 23342c14..e409289c 100644
--- a/src/process/process.rs
+++ b/src/process/process.rs
@@ -42,6 +42,7 @@ impl Process {
             is_user: false,
         }
     }
+
     /// Make the first kernel thread `initproc`
     /// Should be called only once
     pub fn new_init(mc: &mut MemoryController) -> Self {
@@ -58,6 +59,8 @@ impl Process {
         }
     }
 
+    /// Make a new user thread
+    /// The program elf data is placed at [begin, end)
     pub fn new_user(begin: usize, end: usize, mc: &mut MemoryController) -> Self {
         // Parse elf
         let slice = unsafe{ slice::from_raw_parts(begin as *const u8, end - begin) };
@@ -103,6 +106,12 @@ impl Process {
             is_user: true,
         }
     }
+
+    /// Fork
+    pub fn fork(&mut self) -> Self {
+        assert!(self.is_user);
+        unimplemented!()
+    }
 }
 
 use memory::{MemorySet, MemoryArea, PhysAddr, FromToVirtualAddress, EntryFlags};
diff --git a/src/process/processor.rs b/src/process/processor.rs
index df300dcb..79bed747 100644
--- a/src/process/processor.rs
+++ b/src/process/processor.rs
@@ -9,7 +9,7 @@ pub struct Processor {
 }
 
 impl Processor {
-    pub fn new(mc: &mut MemoryController) -> Self {
+    pub fn new() -> Self {
         Processor {
             procs: BTreeMap::<Pid, Process>::new(),
             current_pid: 0,