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SubjectRe: [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@fusionio.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@fromorbit.com

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