diff --git a/os/src/config.rs b/os/src/config.rs
new file mode 100644
index 00000000..ea43a373
--- /dev/null
+++ b/os/src/config.rs
@@ -0,0 +1,7 @@
+// constants for the operating system
+#![allow(unused)]
+
+// about memory management
+pub const PAGE_SIZE: usize = 4096;
+pub const KERNEL_HEAP_SIZE: usize = 16 * 1024 * 1024; // 16MB
+pub const USER_STACK_SIZE: usize = 4 * 1024 * 1024; // 4MB
\ No newline at end of file
diff --git a/os/src/main.rs b/os/src/main.rs
index 6686807e..e4bcce04 100644
--- a/os/src/main.rs
+++ b/os/src/main.rs
@@ -7,6 +7,7 @@
 #[macro_use]
 mod console;
 mod sbi;
+mod config;
 
 use core::arch::global_asm;
 use core::panic::PanicInfo;
diff --git a/os/src/mm/address/.gitkeep b/os/src/mm/address/.gitkeep
new file mode 100644
index 00000000..e69de29b
diff --git a/os/src/mm/allocation/.gitkeep b/os/src/mm/allocation/.gitkeep
new file mode 100644
index 00000000..e69de29b
diff --git a/os/src/mm/global_allocator/.gitkeep b/os/src/mm/global_allocator/.gitkeep
new file mode 100644
index 00000000..e69de29b
diff --git a/os/src/mm/pagetable/.gitkeep b/os/src/mm/pagetable/.gitkeep
new file mode 100644
index 00000000..e69de29b