diff --git a/os/src/mm/frame_allocator.rs b/os/src/mm/frame_allocator.rs
index e467f372..c17385f1 100644
--- a/os/src/mm/frame_allocator.rs
+++ b/os/src/mm/frame_allocator.rs
@@ -11,14 +11,11 @@ pub struct FrameTracker {
 
 impl FrameTracker {
     pub fn new(ppn: PhysPageNum) -> Self {
-        //println!("into FrameTracker::new, ppn = {:?}", ppn);
         // page cleaning
         let bytes_array = ppn.get_bytes_array();
-        //println!("ptr = {:p}, len = {}", bytes_array.as_ptr(), bytes_array.len());
         for i in bytes_array {
             *i = 0;
         }
-        //println!("OK");
         Self { ppn }
     }
 }
@@ -62,12 +59,9 @@ impl FrameAllocator for StackFrameAllocator {
         }
     }
     fn alloc(&mut self) -> Option<PhysPageNum> {
-        //println!("into StackFrameAllocator::alloc()");
         if let Some(ppn) = self.recycled.pop() {
-            //println!("has recycled!");
             Some(ppn.into())
         } else {
-            //println!("run out recycled, current = {}, end = {}!", self.current, self.end);
             if self.current == self.end {
                 None
             } else {
@@ -107,7 +101,6 @@ pub fn init_frame_allocator() {
 }
 
 pub fn frame_alloc() -> Option<FrameTracker> {
-    //println!("into frame_alloc()");
     FRAME_ALLOCATOR
         .lock()
         .alloc()
diff --git a/os/src/mm/memory_set.rs b/os/src/mm/memory_set.rs
index 15b36f79..079d6dba 100644
--- a/os/src/mm/memory_set.rs
+++ b/os/src/mm/memory_set.rs
@@ -124,24 +124,19 @@ impl MemorySet {
     /// Include sections in elf and trampoline and TrapContext and user stack,
     /// also returns user_sp and entry point.
     pub fn from_elf(elf_data: &[u8]) -> (Self, usize, usize) {
-        //println!("into from_elf!");
         let mut memory_set = Self::new_bare();
         // map trampoline
-        //println!("mapping trampoline!");
         memory_set.map_trampoline();
         // map program headers of elf, with U flag
-        //println!("mapping elf!");
         let elf = xmas_elf::ElfFile::new(elf_data).unwrap();
         let elf_header = elf.header;
         let magic = elf_header.pt1.magic;
         assert_eq!(magic, [0x7f, 0x45, 0x4c, 0x46], "invalid elf!");
         let ph_count = elf_header.pt2.ph_count();
-        //println!("ph_count = {}", ph_count);
         let mut max_end_vpn = VirtPageNum(0);
         for i in 0..ph_count {
             let ph = elf.program_header(i).unwrap();
             if ph.get_type().unwrap() == xmas_elf::program::Type::Load {
-                //println!("ph#{},va={},memsz={}", i, ph.virtual_addr(), ph.mem_size());
                 let start_va: VirtAddr = (ph.virtual_addr() as usize).into();
                 let end_va: VirtAddr = ((ph.virtual_addr() + ph.mem_size()) as usize).into();
                 let mut map_perm = MapPermission::U;
@@ -149,16 +144,13 @@ impl MemorySet {
                 if ph_flags.is_read() { map_perm |= MapPermission::R; }
                 if ph_flags.is_write() { map_perm |= MapPermission::W; }
                 if ph_flags.is_execute() { map_perm |= MapPermission::X; }
-                //println!("creating MapArea!");
                 let map_area = MapArea::new(
                     start_va,
                     end_va,
                     MapType::Framed,
                     map_perm,
                 );
-                //println!("end_vpn = {:?}", map_area.vpn_range.get_end());
                 max_end_vpn = map_area.vpn_range.get_end();
-                //println!("pushing MapArea!");
                 memory_set.push(
                     map_area,
                     Some(&elf.input[ph.offset() as usize..(ph.offset() + ph.file_size()) as usize])
@@ -166,13 +158,11 @@ impl MemorySet {
             }
         }
         // map user stack with U flags
-        //println!("mapping user stack!");
         let max_end_va: VirtAddr = max_end_vpn.into();
         let mut user_stack_bottom: usize = max_end_va.into();
         // guard page
         user_stack_bottom += PAGE_SIZE;
         let user_stack_top = user_stack_bottom + USER_STACK_SIZE;
-        //println!("user stack={:#x},{:#x}", user_stack_bottom, user_stack_top);
         memory_set.push(MapArea::new(
             user_stack_bottom.into(),
             user_stack_top.into(),
@@ -180,7 +170,6 @@ impl MemorySet {
             MapPermission::R | MapPermission::W | MapPermission::U,
         ), None);
         // map TrapContext
-        //println!("mapping TrapContext {:#x},{:#x}", TRAP_CONTEXT, TRAMPOLINE);
         memory_set.push(MapArea::new(
             TRAP_CONTEXT.into(),
             TRAMPOLINE.into(),
diff --git a/os/src/mm/page_table.rs b/os/src/mm/page_table.rs
index be3eb378..0ef37db1 100644
--- a/os/src/mm/page_table.rs
+++ b/os/src/mm/page_table.rs
@@ -61,7 +61,6 @@ pub struct PageTable {
 /// Assume that it won't oom when creating/mapping.
 impl PageTable {
     pub fn new() -> Self {
-        //println!("into PageTable::new()");
         let frame = frame_alloc().unwrap();
         PageTable {
             root_ppn: frame.ppn,
@@ -95,8 +94,6 @@ impl PageTable {
         result
     }
     fn find_pte(&self, vpn: VirtPageNum) -> Option<&PageTableEntry> {
-        //println!("into find_pte");
-        //println!("root_ppn = {:?}", self.root_ppn);
         let idxs = vpn.indexes();
         let mut ppn = self.root_ppn;
         let mut result: Option<&PageTableEntry> = None;
@@ -115,7 +112,6 @@ impl PageTable {
     }
     #[allow(unused)]
     pub fn map(&mut self, vpn: VirtPageNum, ppn: PhysPageNum, flags: PTEFlags) {
-        //println!("mapping {:?} {:?}", vpn, ppn);
         let pte = self.find_pte_create(vpn).unwrap();
         assert!(!pte.is_valid(), "vpn {:?} is mapped before mapping", vpn);
         *pte = PageTableEntry::new(ppn, flags | PTEFlags::V);
@@ -127,7 +123,6 @@ impl PageTable {
         *pte = PageTableEntry::empty();
     }
     pub fn translate(&self, vpn: VirtPageNum) -> Option<PageTableEntry> {
-        //println!("into PageTable::translate");
         self.find_pte(vpn)
             .map(|pte| {pte.clone()})
     }
@@ -137,22 +132,17 @@ impl PageTable {
 }
 
 pub fn translated_byte_buffer(token: usize, ptr: *const u8, len: usize) -> Vec<&'static [u8]> {
-    //println!("into translated_byte_buffer!");
     let page_table = PageTable::from_token(token);
     let mut start = ptr as usize;
     let end = start + len;
-    //println!("start={:#x},end={:#x}", start, end);
     let mut v = Vec::new();
     while start < end {
-        //println!("start={:#x}", start);
         let start_va = VirtAddr::from(start);
         let mut vpn = start_va.floor();
-        //println!("vpn={:?}", vpn);
         let ppn = page_table
             .translate(vpn)
             .unwrap()
             .ppn();
-        //println!("ppn={:?}", ppn);
         vpn.step();
         let mut end_va: VirtAddr = vpn.into();
         end_va = end_va.min(VirtAddr::from(end));
diff --git a/os/src/syscall/fs.rs b/os/src/syscall/fs.rs
index c431dfc9..b02e0871 100644
--- a/os/src/syscall/fs.rs
+++ b/os/src/syscall/fs.rs
@@ -4,7 +4,6 @@ use crate::task::current_user_token;
 const FD_STDOUT: usize = 1;
 
 pub fn sys_write(fd: usize, buf: *const u8, len: usize) -> isize {
-    //println!("into sys_write!");
     match fd {
         FD_STDOUT => {
             let buffers = translated_byte_buffer(current_user_token(), buf, len);
diff --git a/os/src/syscall/mod.rs b/os/src/syscall/mod.rs
index fc5254d0..da411680 100644
--- a/os/src/syscall/mod.rs
+++ b/os/src/syscall/mod.rs
@@ -10,7 +10,6 @@ use fs::*;
 use process::*;
 
 pub fn syscall(syscall_id: usize, args: [usize; 3]) -> isize {
-    //println!("into syscall!");
     match syscall_id {
         SYSCALL_WRITE => sys_write(args[0], args[1] as *const u8, args[2]),
         SYSCALL_EXIT => sys_exit(args[0] as i32),
diff --git a/os/src/task/mod.rs b/os/src/task/mod.rs
index 6d51f10a..009829e7 100644
--- a/os/src/task/mod.rs
+++ b/os/src/task/mod.rs
@@ -31,7 +31,6 @@ lazy_static! {
         println!("num_app = {}", num_app);
         let mut tasks: Vec<TaskControlBlock> = Vec::new();
         for i in 0..num_app {
-            println!("creating TCB #{}", i);
             tasks.push(TaskControlBlock::new(
                 get_app_data(i),
                 i,
@@ -49,10 +48,8 @@ lazy_static! {
 
 impl TaskManager {
     fn run_first_task(&self) {
-        println!("into TaskManager::run_first_task");
         self.inner.borrow_mut().tasks[0].task_status = TaskStatus::Running;
         let next_task_cx = self.inner.borrow().tasks[0].get_task_cx_ptr2();
-        println!("next_task_cx={:p} {:#x}", next_task_cx, unsafe { next_task_cx.read_volatile() });
         let _unused: usize = 0;
         unsafe {
             __switch(
diff --git a/os/src/task/task.rs b/os/src/task/task.rs
index 071a814d..8e38635b 100644
--- a/os/src/task/task.rs
+++ b/os/src/task/task.rs
@@ -22,20 +22,15 @@ impl TaskControlBlock {
         self.memory_set.token()
     }
     pub fn new(elf_data: &[u8], app_id: usize) -> Self {
-        //println!("into TCB::new");
         // memory_set with elf program headers/trampoline/trap context/user stack
         let (memory_set, user_sp, entry_point) = MemorySet::from_elf(elf_data);
-        //println!("user_sp={:#x},entry_point={:#}", user_sp, entry_point);
         let trap_cx_ppn = memory_set
             .translate(VirtAddr::from(TRAP_CONTEXT).into())
             .unwrap()
             .ppn();
-        //println!("trap_cx_ppn={:?}", trap_cx_ppn);
         let task_status = TaskStatus::Ready;
         // map a kernel-stack in kernel space
-        //println!("mapping kernel-stack!");
         let (kernel_stack_bottom, kernel_stack_top) = kernel_stack_position(app_id);
-        //println!("kernel_stack={:#x},{:#x}", kernel_stack_bottom, kernel_stack_top);
         KERNEL_SPACE
             .lock()
             .insert_framed_area(
@@ -44,10 +39,7 @@ impl TaskControlBlock {
                 MapPermission::R | MapPermission::W,
             );
         let task_cx_ptr = (kernel_stack_top - core::mem::size_of::<TaskContext>()) as *mut TaskContext;
-        //println!("task_cx size={}", core::mem::size_of::<TaskContext>());
-        //println!("init task_cx, ptr={:p}", task_cx_ptr);
         unsafe { *task_cx_ptr = TaskContext::goto_trap_return(); }
-        //println!("after init task_cx");
         let task_control_block = Self {
             task_cx_ptr: task_cx_ptr as usize,
             task_status,
@@ -56,7 +48,6 @@ impl TaskControlBlock {
             base_size: user_sp,
         };
         // prepare TrapContext in user space
-        //println!("preparing trap_cx");
         let trap_cx = task_control_block.get_trap_cx();
         *trap_cx = TrapContext::app_init_context(
             entry_point,
diff --git a/os/src/trap/mod.rs b/os/src/trap/mod.rs
index 839ed049..46e113bb 100644
--- a/os/src/trap/mod.rs
+++ b/os/src/trap/mod.rs
@@ -52,14 +52,12 @@ pub fn enable_timer_interrupt() {
 
 #[no_mangle]
 pub fn trap_handler() -> ! {
-    //println!("into trap_handler!");
     set_kernel_trap_entry();
     let cx = current_trap_cx();
     let scause = scause::read();
     let stval = stval::read();
     match scause.cause() {
         Trap::Exception(Exception::UserEnvCall) => {
-            //println!("found UserEnvCall!");
             cx.sepc += 4;
             cx.x[10] = syscall(cx.x[17], [cx.x[10], cx.x[11], cx.x[12]]) as usize;
         }
@@ -86,17 +84,13 @@ pub fn trap_handler() -> ! {
 #[no_mangle]
 pub fn trap_return() -> ! {
     set_user_trap_entry();
-    //println!("into trap_return");
     let trap_cx_ptr = TRAP_CONTEXT;
     let user_satp = current_user_token();
-    //println!("trap_cx_ptr={:#x}, user_satp={:#x}", trap_cx_ptr, user_satp);
     extern "C" {
         fn __alltraps();
         fn __restore();
     }
     let restore_va = __restore as usize - __alltraps as usize + TRAMPOLINE;
-    //println!("__alltraps={:#x},__restore={:#x}", __alltraps as usize, __restore as usize);
-    //println!("restore_va={:#x}", restore_va);
     unsafe {
         llvm_asm!("jr $0" :: "r"(restore_va), "{a0}"(trap_cx_ptr), "{a1}"(user_satp) :: "volatile");
     }