xfs directory quota doesn't work

Question

I have two tasks and I want to run them in different directory and limit the directory's size. I use xfs's project quota to achieve this.

I follow the steps from here:https://solidlinux.wordpress.com/2012/12/09/xfs-quota-managament/

here is detail of my two config files

/etc/projects:

11:/home/xiameng.xm/xfs_dir/task1
12:/home/xiameng.xm/xfs_dir/task2

/etc/projid:

task1:11
task2:12

and here is my step:

touch test_xfs
dd if=/dev/zero of=test_xfs bs=100M count=1
mkfs.xfs test_xfs

mkdir xfs_dir
mount test_xfs ./xfs_dir -o pquota,loop

xfs_quota -xc 'project –s task1' /home/xiameng.xm/xfs_dir
xfs_quota -xc 'project –s task2' /home/xiameng.xm/xfs_dir

xfs_quota -x -c 'limit -p bhard=2m task1' /home/xiameng.xm/xfs_dir
xfs_quota -x -c 'limit -p bhard=10m task2' /home/xiameng.xm/xfs_dir

here is the output of xfs_quota -x -c 'report /home/xiameng.xm/xfs_dir'

Project quota on /home/xiameng.xm/xfs_dir (/dev/loop1)
                               Blocks
Project ID       Used       Soft       Hard    Warn/Grace
---------- --------------------------------------------------
task1               0          0       2048     00 [--------]
task2               0          0      10240     00 [--------]

the question is no mater how large I create a file in ./xfs_dir/task1 or ./xfs_dir/task2, it succeeds!

The quota limit doesn't work!