diff --git a/rcore-fs-sefs/src/lib.rs b/rcore-fs-sefs/src/lib.rs
index 604d7d2..1ec5b9d 100644
--- a/rcore-fs-sefs/src/lib.rs
+++ b/rcore-fs-sefs/src/lib.rs
@@ -18,7 +18,7 @@ use bitvec::BitVec;
 use rcore_fs::dev::TimeProvider;
 use rcore_fs::dirty::Dirty;
 use rcore_fs::vfs::{self, FileSystem, FsError, INode, Timespec};
-//use log::*;
+use log::*;
 use spin::RwLock;
 
 use self::dev::*;
@@ -143,14 +143,16 @@ impl INodeImpl {
 
 impl vfs::INode for INodeImpl {
     fn read_at(&self, offset: usize, buf: &mut [u8]) -> vfs::Result<usize> {
-        if self.disk_inode.read().type_ != FileType::File {
+        let type_ = self.disk_inode.read().type_;
+        if type_ != FileType::File && type_ != FileType::SymLink {
             return Err(FsError::NotFile);
         }
         let len = self.file.read_at(buf, offset)?;
         Ok(len)
     }
     fn write_at(&self, offset: usize, buf: &[u8]) -> vfs::Result<usize> {
-        if self.disk_inode.read().type_ != FileType::File {
+        let type_ = self.disk_inode.read().type_;
+        if type_ != FileType::File && type_ != FileType::SymLink {
             return Err(FsError::NotFile);
         }
         let len = self.file.write_at(buf, offset)?;
@@ -170,7 +172,7 @@ impl vfs::INode for INodeImpl {
             dev: 0,
             inode: self.id,
             size: match disk_inode.type_ {
-                FileType::File => disk_inode.size as usize,
+                FileType::File | FileType::SymLink => disk_inode.size as usize,
                 FileType::Dir => disk_inode.blocks as usize,
                 _ => panic!("Unknown file type"),
             },
@@ -221,7 +223,8 @@ impl vfs::INode for INodeImpl {
         Ok(())
     }
     fn resize(&self, len: usize) -> vfs::Result<()> {
-        if self.disk_inode.read().type_ != FileType::File {
+        let type_ = self.disk_inode.read().type_;
+        if type_ != FileType::File && type_ != FileType::SymLink {
             return Err(FsError::NotFile);
         }
         self.file.set_len(len)?;
@@ -232,6 +235,7 @@ impl vfs::INode for INodeImpl {
         let type_ = match type_ {
             vfs::FileType::File => FileType::File,
             vfs::FileType::Dir => FileType::Dir,
+            vfs::FileType::SymLink => FileType::SymLink,
             _ => return Err(vfs::FsError::InvalidParam),
         };
         let info = self.metadata()?;
@@ -464,11 +468,18 @@ impl SEFS {
         if !super_block.check() {
             return Err(FsError::WrongFs);
         }
-        let free_map = meta_file.load_struct::<[u8; BLKSIZE]>(BLKN_FREEMAP)?;
+
+        // load free map
+        let mut free_map = BitVec::with_capacity(BLKBITS * super_block.groups as usize);
+        unsafe { free_map.set_len(BLKBITS * super_block.groups as usize); }
+        for i in 0..super_block.groups as usize {
+            let block_id = Self::get_freemap_block_id_of_group(i);
+            meta_file.read_block(block_id, &mut free_map.as_mut()[BLKSIZE * i..BLKSIZE * (i+1)])?;
+        }
 
         Ok(SEFS {
             super_block: RwLock::new(Dirty::new(super_block)),
-            free_map: RwLock::new(Dirty::new(BitVec::from(free_map.as_ref()))),
+            free_map: RwLock::new(Dirty::new(free_map)),
             inodes: RwLock::new(BTreeMap::new()),
             device,
             meta_file,
@@ -488,6 +499,7 @@ impl SEFS {
             magic: MAGIC,
             blocks: blocks as u32,
             unused_blocks: blocks as u32 - 2,
+            groups: 1,
         };
         let free_map = {
             let mut bitset = BitVec::with_capacity(BLKBITS);
@@ -538,15 +550,22 @@ impl SEFS {
     /// Allocate a block, return block id
     fn alloc_block(&self) -> Option<usize> {
         let mut free_map = self.free_map.write();
-        let id = free_map.alloc();
-        if let Some(block_id) = id {
-            let mut super_block = self.super_block.write();
-            if super_block.unused_blocks == 0 {
-                free_map.set(block_id, true);
-                return None;
-            }
-            super_block.unused_blocks -= 1; // will not underflow
-        }
+        let mut super_block = self.super_block.write();
+        let id = free_map.alloc().or_else(|| {
+            // allocate a new group
+            let new_group_id = super_block.groups as usize;
+            super_block.groups += 1;
+            super_block.blocks += BLKBITS as u32;
+            super_block.unused_blocks += BLKBITS as u32 - 1;
+            self.meta_file.set_len(super_block.groups as usize * BLKBITS * BLKSIZE)
+                .expect("failed to extend meta file");
+            free_map.extend(core::iter::repeat(true).take(BLKBITS));
+            free_map.set(Self::get_freemap_block_id_of_group(new_group_id), false);
+            // allocate block again
+            free_map.alloc()
+        });
+        assert!(id.is_some(), "allocate block should always success");
+        super_block.unused_blocks -= 1;
         id
     }
     /// Free a block
@@ -621,29 +640,39 @@ impl SEFS {
             inodes.remove(&id);
         }
     }
+    fn get_freemap_block_id_of_group(group_id: usize) -> usize {
+        BLKBITS * group_id + BLKN_FREEMAP
+    }
 }
 
 impl vfs::FileSystem for SEFS {
     /// Write back super block if dirty
     fn sync(&self) -> vfs::Result<()> {
+        // sync super_block
         let mut super_block = self.super_block.write();
         if super_block.dirty() {
             self.meta_file
                 .write_all_at(super_block.as_buf(), BLKSIZE * BLKN_SUPER)?;
             super_block.sync();
         }
+        // sync free_map
         let mut free_map = self.free_map.write();
         if free_map.dirty() {
-            self.meta_file
-                .write_all_at(free_map.as_buf(), BLKSIZE * BLKN_FREEMAP)?;
+            for i in 0..super_block.groups as usize {
+                let slice = &free_map.as_ref()[BLKSIZE * i..BLKSIZE * (i+1)];
+                self.meta_file
+                    .write_all_at(slice, BLKSIZE * Self::get_freemap_block_id_of_group(i))?;
+            }
             free_map.sync();
         }
+        // sync all INodes
         self.flush_weak_inodes();
         for inode in self.inodes.read().values() {
             if let Some(inode) = inode.upgrade() {
                 inode.sync_all()?;
             }
         }
+        self.meta_file.flush()?;
         Ok(())
     }
 
@@ -670,7 +699,7 @@ impl Drop for SEFS {
     /// Auto sync when drop
     fn drop(&mut self) {
         self.sync()
-            .expect("Failed to sync when dropping the SimpleFileSystem");
+            .expect("Failed to sync when dropping the SEFS");
     }
 }
 
@@ -705,6 +734,7 @@ impl From<FileType> for vfs::FileType {
         match t {
             FileType::File => vfs::FileType::File,
             FileType::Dir => vfs::FileType::Dir,
+            FileType::SymLink => vfs::FileType::SymLink,
             _ => panic!("unknown file type"),
         }
     }
diff --git a/rcore-fs-sefs/src/structs.rs b/rcore-fs-sefs/src/structs.rs
index 59b14a4..14e1f55 100644
--- a/rcore-fs-sefs/src/structs.rs
+++ b/rcore-fs-sefs/src/structs.rs
@@ -16,6 +16,8 @@ pub struct SuperBlock {
     pub blocks: u32,
     /// number of unused blocks in fs
     pub unused_blocks: u32,
+    /// number of block groups
+    pub groups: u32,
 }
 
 /// On-disk inode
@@ -115,8 +117,6 @@ pub const BLKSIZE_LOG2: u8 = 7;
 pub const MAX_INFO_LEN: usize = 31;
 /// max length of filename
 pub const MAX_FNAME_LEN: usize = 255;
-/// max file size (128M)
-pub const MAX_FILE_SIZE: usize = 1024 * 1024 * 128;
 /// block the superblock lives in
 pub const BLKN_SUPER: BlockId = 0;
 /// location of the root dir inode
@@ -139,7 +139,7 @@ pub enum FileType {
     Invalid = 0,
     File = 1,
     Dir = 2,
-    Link = 3,
+    SymLink = 3,
 }
 
 const_assert!(o1; size_of::<SuperBlock>() <= BLKSIZE);
diff --git a/sefs-fuse/enclave/src/lib.rs b/sefs-fuse/enclave/src/lib.rs
index 976bc66..141414c 100644
--- a/sefs-fuse/enclave/src/lib.rs
+++ b/sefs-fuse/enclave/src/lib.rs
@@ -45,7 +45,6 @@ use std::io::{Read, Seek, SeekFrom, Write};
 use std::path::PathBuf;
 use std::sgxfs::{OpenOptions, SgxFile};
 use std::sync::{SgxMutex as Mutex, SgxRwLock as RwLock};
-use std::vec::Vec;
 use sgx_types::sgx_key_128bit_t;
 
 #[no_mangle]
@@ -147,7 +146,16 @@ pub extern "C" fn ecall_file_set_len(fd: usize, len: usize) -> i32 {
         let mut rest_len = len - current_len;
         while rest_len != 0 {
             let l = rest_len.min(0x1000);
-            try_io!(file.write(&ZEROS[..l]));
+            let ret = file.write(&ZEROS[..l]);
+            if let Err(e) = ret {
+                if e.raw_os_error().unwrap() == 12 {
+                    warn!("Error 12: \"Cannot allocate memory\". Clear cache and try again.");
+                    try_io!(file.clear_cache());
+                    try_io!(file.write(&ZEROS[..l]));
+                } else {
+                    try_io!(Err(e));
+                }
+            }
             rest_len -= l;
         }
         // NOTE: Don't try to write a large slice at once.