Btrfs: implement unlocked dio write (38851cc1) · Commits · 戴 / test

This idea is from ext4. By this patch, we can make the dio write parallel, and improve the performance. But because we can not update isize without i_mutex, the unlocked dio write just can be done in front of the EOF. We needn't worry about the race between dio write and truncate, because the truncate need wait untill all the dio write end. And we also needn't worry about the race between dio write and punch hole, because we have extent lock to protect our operation. I ran fio to test the performance of this feature. == Hardware == CPU: Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz Mem: 2GB SSD: Intel X25-M 120GB (Test Partition: 60GB) == config file == [global] ioengine=psync direct=1 bs=4k size=32G runtime=60 directory=/mnt/btrfs/ filename=testfile group_reporting thread [file1] numjobs=1 # 2 4 rw=randwrite == result (KBps) == write 1 2 4 lock 24936 24738 24726 nolock 24962 30866 32101 == result (iops) == write 1 2 4 lock 6234 6184 6181 nolock 6240 7716 8025 Signed-off-by:

Miao Xie <miaox@cn.fujitsu.com> Signed-off-by:

Josef Bacik <jbacik@fusionio.com>

fs/btrfs/inode.c

+23 −12

Original line number	Diff line number	Diff line
		@@ -6677,28 +6677,36 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
		struct inode *inode = file->f_mapping->host;
		size_t count = 0;
		int flags = 0;
		bool wakeup = false;
		bool wakeup = true;
		bool relock = false;
		ssize_t ret;

		if (check_direct_IO(BTRFS_I(inode)->root, rw, iocb, iov,
		offset, nr_segs))
		return 0;

		atomic_inc(&inode->i_dio_count);
		smp_mb__after_atomic_inc();

		if (rw & WRITE) {
		count = iov_length(iov, nr_segs);
		/*
		* If the write DIO is beyond the EOF, we need update
		* the isize, but it is protected by i_mutex. So we can
		* not unlock the i_mutex at this case.
		*/
		if (offset + count <= inode->i_size) {
		mutex_unlock(&inode->i_mutex);
		relock = true;
		}
		ret = btrfs_delalloc_reserve_space(inode, count);
		if (ret)
		return ret;
		} else {
		atomic_inc(&inode->i_dio_count);
		smp_mb__after_atomic_inc();
		if (unlikely(test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
		goto out;
		} else if (unlikely(test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
		&BTRFS_I(inode)->runtime_flags))) {
		inode_dio_done(inode);
		flags = DIO_LOCKING \| DIO_SKIP_HOLES;
		} else {
		wakeup = true;
		}
		wakeup = false;
		}

		ret = __blockdev_direct_IO(rw, iocb, inode,
		@@ -6717,8 +6725,11 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
		}
		btrfs_delalloc_release_metadata(inode, 0);
		}
		out:
		if (wakeup)
		inode_dio_done(inode);
		if (relock)
		mutex_lock(&inode->i_mutex);

		return ret;
		}

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