linux-kernel - Re: [PATCH 07/10] fs: make generic file read/write functions plug

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Message-ID: <20110124035717.GC16267@dastard>
Date:	Mon, 24 Jan 2011 14:57:17 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: [PATCH 07/10] fs: make generic file read/write functions plug

On Sat, Jan 22, 2011 at 01:17:26AM +0000, Jens Axboe wrote:
> Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
> ---
>  mm/filemap.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
.....
> @@ -2432,11 +2436,13 @@ ssize_t generic_file_aio_write(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;
>  
>  	BUG_ON(iocb->ki_pos != pos);
>  
>  	mutex_lock(&inode->i_mutex);
> +	blk_start_plug(&plug);
>  	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
>  	mutex_unlock(&inode->i_mutex);
>  
> @@ -2447,6 +2453,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
>  		if (err < 0 && ret > 0)
>  			ret = err;
>  	}
> +	blk_finish_plug(&plug);
>  	return ret;
>  }
>  EXPORT_SYMBOL(generic_file_aio_write);

Why do you want to plug all writes? For non-synchronous buffered
writes we won't be doing any IO, so why woul dwe want to plug and
unplug in that case? Shouldn't the plug/unplug be places in
.writepage for the buffered writeback case (which would handle sync
writes, too)?

Also, what is the impact of not plugging here? You change
generic_file_aio_write, but filesystems like XFS supply their own
.aio_write method and hence woul dneed some kind of change, too?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
--
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