diff --git a/crate/memory/src/swap/mod.rs b/crate/memory/src/swap/mod.rs
index d568f91..088f9c3 100644
--- a/crate/memory/src/swap/mod.rs
+++ b/crate/memory/src/swap/mod.rs
@@ -259,6 +259,7 @@ impl<T: PageTable, M: SwapManager, S: Swapper> SwapExt<T, M, S> {
     **  @retval bool                 whether swap in happens.
     */
     pub fn page_fault_handler<T2: InactivePageTable>(&mut self, pt: *mut T2, addr: VirtAddr, alloc_frame: impl FnOnce() -> PhysAddr) -> bool {
+        // now we didn't attach the cow so the present will be false when swapped(), to enable the cow some changes will be needed
         if !self.page_table.get_entry(addr).swapped() {
             return false;
         }
diff --git a/docs/OSTrain2018docs-g4/expr3/report.md b/docs/OSTrain2018docs-g4/expr3/report.md
new file mode 100644
index 0000000..a1be136
--- /dev/null
+++ b/docs/OSTrain2018docs-g4/expr3/report.md
@@ -0,0 +1,9 @@
+# Rust OS 教学lab实验的制作 基础功能完善
+## 1 内存管理
+@刘辰屹
+## 2 进程管理
+@陈秋昊
+## 3 同步互斥
+@陈秋昊
+## 4 文件系统
+@朱书聪
\ No newline at end of file
diff --git a/kernel/src/memory.rs b/kernel/src/memory.rs
index 1badead..23070e9 100644
--- a/kernel/src/memory.rs
+++ b/kernel/src/memory.rs
@@ -7,7 +7,6 @@ use ucore_memory::{*, paging::PageTable};
 use ucore_memory::cow::CowExt;
 pub use ucore_memory::memory_set::{MemoryArea, MemoryAttr, MemorySet as MemorySet_, Stack};
 use ucore_memory::swap::*;
-use alloc::collections::VecDeque;
 use process::processor;
 
 pub type MemorySet = MemorySet_<InactivePageTable0>;