Re: Re: [PATCH 1/2] fs/block-dev.c:fix performance regression in O_DIRECT writes to md block devices.

[majianpeng <majianpeng@gmail.com>]

On 2012-07-16 13:21 NeilBrown <neilb@suse.de> Wrote:
>On Mon, 16 Jul 2012 09:30:50 +0800 majianpeng <majianpeng@gmail.com> wrote:
>
>> 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 <majianpeng@gmail.com>
>> ---
>>  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.