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SubjectRe: [PATCH] fix readahead pipeline break caused by block plug
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On Tue, 2012-01-31 at 18:34 +0800, Wu Fengguang wrote:
> I'd like to propose a sister patch on the write part. It may not be
> as easy to measure any performance impacts of it, but I'll try.
I did think about it, the write case doesn't matter because we didn't do
real IO there.
I can do another patch to cleanup the code (moving it to direct_io),
sounds ok?

> ---
> Subject: remove plugging at buffered write time
> Date: Tue Jan 31 18:25:48 CST 2012
>
> Buffered write(2) is not directly tied to IO, so no need to handle plug
> in generic_file_aio_write().
>
> CC: Jens Axboe <axboe@kernel.dk>
> CC: Li Shaohua <shaohua.li@intel.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> mm/filemap.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> --- linux-next.orig/mm/filemap.c 2012-01-31 18:23:52.000000000 +0800
> +++ linux-next/mm/filemap.c 2012-01-31 18:25:38.000000000 +0800
> @@ -2267,6 +2267,7 @@ generic_file_direct_write(struct kiocb *
> struct file *file = iocb->ki_filp;
> struct address_space *mapping = file->f_mapping;
> struct inode *inode = mapping->host;
> + struct blk_plug plug;
> ssize_t written;
> size_t write_len;
> pgoff_t end;
> @@ -2301,7 +2302,9 @@ generic_file_direct_write(struct kiocb *
> }
> }
>
> + blk_start_plug(&plug);
> written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
> + blk_finish_plug(&plug);
>
> /*
> * Finally, try again to invalidate clean pages which might have been
> @@ -2610,13 +2613,11 @@ ssize_t generic_file_aio_write(struct ki
> {
> 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);
>
> @@ -2627,7 +2628,6 @@ ssize_t generic_file_aio_write(struct ki
> if (err < 0 && ret > 0)
> ret = err;
> }
> - blk_finish_plug(&plug);
> return ret;
> }
> EXPORT_SYMBOL(generic_file_aio_write);




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