diff --git a/kernel/src/arch/x86_64/interrupt/fast_syscall.rs b/kernel/src/arch/x86_64/interrupt/fast_syscall.rs
index 69170ac..89ff76f 100644
--- a/kernel/src/arch/x86_64/interrupt/fast_syscall.rs
+++ b/kernel/src/arch/x86_64/interrupt/fast_syscall.rs
@@ -10,9 +10,9 @@ pub fn init() {
             *flags |= EferFlags::SYSTEM_CALL_EXTENSIONS;
         });
 
-        let mut star = Msr::new(0xC0000081);
-        let mut lstar = Msr::new(0xC0000082);
-        let mut sfmask = Msr::new(0xC0000084);
+        let mut star = Msr::new(0xC0000081);   // legacy mode SYSCALL target
+        let mut lstar = Msr::new(0xC0000082);  // long mode SYSCALL target
+        let mut sfmask = Msr::new(0xC0000084); // EFLAGS mask for syscall
 
         // flags to clear on syscall
         // copy from Linux 5.0
diff --git a/kernel/src/arch/x86_64/mod.rs b/kernel/src/arch/x86_64/mod.rs
index 4b5f56c..bec0e26 100644
--- a/kernel/src/arch/x86_64/mod.rs
+++ b/kernel/src/arch/x86_64/mod.rs
@@ -40,26 +40,33 @@ pub extern "C" fn _start(boot_info: &'static BootInfo) -> ! {
     memory::init(boot_info);
 
     // Now heap is available
-    gdt::init();
 
+    // Init GDT
+    gdt::init();
+    //get local apic id of cpu
     cpu::init();
-
+    // Use IOAPIC instead of PIC, use APIC Timer instead of PIT, init serial&keyboard in x86_64
     driver::init();
-
+    // init pci/bus-based devices ,e.g. Intel 10Gb NIC, ...
     crate::drivers::init();
-
+    // init cpu scheduler and process manager, and add user shell app in process manager
     crate::process::init();
-
+    //wake up other CPUs
     AP_CAN_INIT.store(true, Ordering::Relaxed);
-
+    //call the first main function in kernel.
     crate::kmain();
 }
 
 /// The entry point for other processors
 fn other_start() -> ! {
+    // Init trap handling.
     idt::init();
+    // init gdt
     gdt::init();
+    // init local apic
     cpu::init();
+    // setup fast syscall in xv6-64
     interrupt::fast_syscall::init();
+    //call the first main function in kernel.
     crate::kmain();
 }
diff --git a/kernel/src/memory.rs b/kernel/src/memory.rs
index 482f96e..fa0c2dc 100644
--- a/kernel/src/memory.rs
+++ b/kernel/src/memory.rs
@@ -1,3 +1,17 @@
+//! Define the FrameAllocator for physical memory
+//! x86_64      --  64GB
+//! AARCH64/MIPS/RV --  1GB
+//! K210(rv64)  --  8MB
+//! NOTICE:
+//! type FrameAlloc = bitmap_allocator::BitAllocXXX
+//! KSTACK_SIZE         -- 16KB
+//!
+//! KERNEL_HEAP_SIZE:
+//! x86-64              -- 32MB
+//! AARCH64/RV64        -- 8MB
+//! MIPS/RV32           -- 2MB
+//! mipssim/malta(MIPS) -- 10MB
+
 use super::HEAP_ALLOCATOR;
 pub use crate::arch::paging::*;
 use crate::consts::MEMORY_OFFSET;
@@ -85,17 +99,17 @@ pub fn dealloc_frame(target: usize) {
 }
 
 pub struct KernelStack(usize);
-const STACK_SIZE: usize = 0x4000;
+const KSTACK_SIZE: usize = 0x4000; //16KB
 
 impl KernelStack {
     pub fn new() -> Self {
         use alloc::alloc::{alloc, Layout};
         let bottom =
-            unsafe { alloc(Layout::from_size_align(STACK_SIZE, STACK_SIZE).unwrap()) } as usize;
+            unsafe { alloc(Layout::from_size_align(KSTACK_SIZE, KSTACK_SIZE).unwrap())} as usize;
         KernelStack(bottom)
     }
     pub fn top(&self) -> usize {
-        self.0 + STACK_SIZE
+        self.0 + KSTACK_SIZE
     }
 }
 
@@ -105,7 +119,7 @@ impl Drop for KernelStack {
         unsafe {
             dealloc(
                 self.0 as _,
-                Layout::from_size_align(STACK_SIZE, STACK_SIZE).unwrap(),
+                Layout::from_size_align(KSTACK_SIZE, KSTACK_SIZE).unwrap(),
             );
         }
     }
diff --git a/kernel/src/process/mod.rs b/kernel/src/process/mod.rs
index 516d29e..d9908a9 100644
--- a/kernel/src/process/mod.rs
+++ b/kernel/src/process/mod.rs
@@ -20,7 +20,7 @@ pub fn init() {
         }
     }
 
-    crate::shell::run_user_shell();
+    crate::shell::add_user_shell();
 
     info!("process: init end");
 }
diff --git a/kernel/src/shell.rs b/kernel/src/shell.rs
index f604729..fc4bdce 100644
--- a/kernel/src/shell.rs
+++ b/kernel/src/shell.rs
@@ -8,7 +8,7 @@ use alloc::vec::Vec;
 
 
 #[cfg(not(feature = "run_cmdline"))]
-pub fn run_user_shell() {
+pub fn add_user_shell() {
 /// the busybox of alpine linux can not transfer env vars into child process
 /// Now we use busybox from
 /// https://raw.githubusercontent.com/docker-library/busybox/82bc0333a9ae148fbb4246bcbff1487b3fc0c510/musl/busybox.tar.xz -O busybox.tar.xz
@@ -43,7 +43,7 @@ pub fn run_user_shell() {
 }
 
 #[cfg(feature = "run_cmdline")]
-pub fn run_user_shell() {
+pub fn add_user_shell() {
     let cmdline = CMDLINE.read();
     let inode = ROOT_INODE.lookup(&cmdline).unwrap();
     let data = inode.read_as_vec().unwrap();