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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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