From: Daeho Jeong <daehojeong@xxxxxxxxxx>
writepages() can be concurrently invoked for the same file by different
threads such as a thread fsyncing the file and a kworker kernel thread.
So, changing i_compr_blocks without protection is racy and we need to
protect it by changing it with atomic type value. Plus, we don't need
a 64bit value for i_compr_blocks, so just we will use a atomic value,
not atomic64.
Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>