fs/block-dev.c:fix performance regression in O_DIRECT writes to md block devices

For regular file, write operaion used blk_plug function.But for block
file,write operation did not use blk_plug.
This patch is also for write-cache mode for block-device.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1e519195d45bd1ab466f8b7ee12505f35a45d271..38e721b35d45388cb0febed8021a02277a4a2f1b 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1578,10 +1578,12 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
                         unsigned long nr_segs, loff_t pos)
 {
        struct file *file = iocb->ki_filp;
+       struct blk_plug plug;
        ssize_t ret;
 
        BUG_ON(iocb->ki_pos != pos);
 
+       blk_start_plug(&plug);
        ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
        if (ret > 0 || ret == -EIOCBQUEUED) {
                ssize_t err;
@@ -1590,6 +1592,7 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
                if (err < 0 && ret > 0)
                        ret = err;
        }
+       blk_finish_plug(&plug);
        return ret;
 }
 EXPORT_SYMBOL_GPL(blkdev_aio_write);