f2fs: show the max number of atomic operations

This patch adds to show the max number of atomic operations which are
conducting concurrently.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -243,6 +243,7 @@ void drop_inmem_pages(struct inode *inode)
 	struct f2fs_inode_info *fi = F2FS_I(inode);
 
 	clear_inode_flag(inode, FI_ATOMIC_FILE);
+	stat_dec_atomic_write(inode);
 
 	mutex_lock(&fi->inmem_lock);
 	__revoke_inmem_pages(inode, &fi->inmem_pages, true, false);