Re: [PATCH 1/2] fs/block-dev.c:fix performance regression in O_DIRECT writes to md block devices.
From: NeilBrown <hidden>
Date: 2012-07-16 05:21:11
Also in:
linux-fsdevel
On Mon, 16 Jul 2012 09:30:50 +0800 majianpeng [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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
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