diff --git a/os/src/config.rs b/os/src/config.rs
index c4b90f77..06efeb35 100644
--- a/os/src/config.rs
+++ b/os/src/config.rs
@@ -1,7 +1,7 @@
 pub const USER_STACK_SIZE: usize = 4096 * 2;
 pub const KERNEL_STACK_SIZE: usize = 4096 * 2;
-pub const KERNEL_HEAP_SIZE: usize = 0x30_0000;
-pub const MEMORY_END: usize = 0x80800000;
+pub const KERNEL_HEAP_SIZE: usize = 0x20_0000;
+pub const MEMORY_END: usize = 0x80600000;
 pub const PAGE_SIZE: usize = 0x1000;
 pub const PAGE_SIZE_BITS: usize = 0xc;
 
diff --git a/user/src/bin/forktest.rs b/user/src/bin/forktest.rs
index dcf8859e..fea6967c 100644
--- a/user/src/bin/forktest.rs
+++ b/user/src/bin/forktest.rs
@@ -6,7 +6,7 @@ extern crate user_lib;
 
 use user_lib::{fork, wait, exit};
 
-const MAX_CHILD: usize = 20;
+const MAX_CHILD: usize = 40;
 
 #[no_mangle]
 pub fn main() -> i32 {
diff --git a/user/src/bin/forktest2.rs b/user/src/bin/forktest2.rs
index f47e73f2..493fccd8 100644
--- a/user/src/bin/forktest2.rs
+++ b/user/src/bin/forktest2.rs
@@ -4,9 +4,9 @@
 #[macro_use]
 extern crate user_lib;
 
-use user_lib::{fork, wait, get_time, getpid, exit, yield_,};
+use user_lib::{fork, wait, getpid, exit, sleep, get_time};
 
-static NUM: usize = 13;
+static NUM: usize = 30;
 
 #[no_mangle]
 pub fn main() -> i32 {
@@ -15,11 +15,9 @@ pub fn main() -> i32 {
         if pid == 0 {
             let current_time = get_time();
             let sleep_length = (current_time as i32 as isize) * (current_time as i32 as isize) % 1000 + 1000;
-            println!("Subprocess {} sleep for {} ms", getpid(), sleep_length);
-            while get_time() < current_time + sleep_length {
-                yield_();
-            }
-            println!("Subprocess {} OK!", getpid());
+            println!("pid {} sleep for {} ms", getpid(), sleep_length);
+            sleep(sleep_length as usize);
+            println!("pid {} OK!", getpid());
             exit(0);
         }
     }
diff --git a/user/src/bin/forktree.rs b/user/src/bin/forktree.rs
index 397e5e05..26954b7a 100644
--- a/user/src/bin/forktree.rs
+++ b/user/src/bin/forktree.rs
@@ -6,7 +6,7 @@ extern crate user_lib;
 
 use user_lib::{sleep, getpid, fork, exit, yield_};
 
-const DEPTH: usize = 3;
+const DEPTH: usize = 4;
 
 fn fork_child(cur: &str, branch: char) {
     let mut next = [0u8; DEPTH + 1];
diff --git a/user/src/bin/matrix.rs b/user/src/bin/matrix.rs
index d5f946b8..95904337 100644
--- a/user/src/bin/matrix.rs
+++ b/user/src/bin/matrix.rs
@@ -6,7 +6,7 @@ extern crate user_lib;
 
 use user_lib::{fork, wait, yield_, exit, getpid, get_time};
 
-static NUM: usize = 20;
+static NUM: usize = 35;
 const N: usize = 10;
 static P: i32 = 10007;
 type Arr = [[i32; N]; N];
diff --git a/user/src/bin/user_shell.rs b/user/src/bin/user_shell.rs
index 6aa8e31f..973f8901 100644
--- a/user/src/bin/user_shell.rs
+++ b/user/src/bin/user_shell.rs
@@ -32,7 +32,7 @@ pub fn main() -> i32 {
                         // child process
                         if exec(line.as_str()) == -1 {
                             println!("Error when executing!");
-                            return 0;
+                            return -4;
                         }
                         unreachable!();
                     } else {