On 2012-07-16 13:21 NeilBrown [off-list ref] Wrote:

On Mon, 16 Jul 2012 09:30:50 +0800 majianpeng [off-list ref] wrote:

quoted

For regular file, write operaion used blk_plug function.But for block
file,write operation did not use blk_plug.

Signed-off-by: Jianpeng Ma <redacted>
---
 fs/block_dev.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c2bbe1f..22cd436 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c

@@ -215,9 +215,14 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_mapping->host;
+	struct blk_plug plug;
+	ssize_t ret;
 
-	return __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iov, offset,
+	blk_start_plug(&plug);
+	ret =  __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iov, offset,
 				    nr_segs, blkdev_get_blocks, NULL, NULL, 0);
+	blk_finish_plug(&plug);
+	return ret;
 }
 
 int __sync_blockdev(struct block_device *bdev, int wait)

[cc:ing Jens Axboe]

I think we do need something like this, but I don't think this is the right
place for it.

For normal filesystem writes, the blk_{start,finish}_plug calls are in
generic_file_aio_write which is the "aio_write" function, or is called by it.
aio_write calls generic_file_aio_write, calls blk_start_plug, call
__generic_file_aio_write.

For block devices we bypass the generic_file_aio_write:

aio_write calls blkdev_aio_write calls __generic_file_aio_write - without
calling blk_start_plug.
So I think the calls to blk_start_plug and blk_finish_plug should go in
blkdev_aio_write.  i.e. blkdev_aio_write should be made to look more like
generic_file_aio_write (just without the mutex_lock/unlock).

If you redo the patch like that and test it I'll happily add my Reviewed-by.

I suspect it should be merged through Jens' tree.

Thanks,
NeilBrown

Thanks, i'll do it and resend the patch.