linux-kernel - Re: [PATCH v3 41/49] xfs: convert to bio_for_each_segment_all

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Date:   Tue, 8 Aug 2017 09:32:32 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...com>, Christoph Hellwig <hch@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH v3 41/49] xfs: convert to bio_for_each_segment_all_sp()

On Tue, Aug 08, 2017 at 04:45:40PM +0800, Ming Lei wrote:

Sure would be nice to have a changelog explaining why we're doing this.

> Cc: "Darrick J. Wong" <darrick.wong@...cle.com>
> Cc: linux-xfs@...r.kernel.org
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>  fs/xfs/xfs_aops.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 6bf120bb1a17..94df43dcae0b 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -139,6 +139,7 @@ xfs_destroy_ioend(
>  	for (bio = &ioend->io_inline_bio; bio; bio = next) {
>  		struct bio_vec	*bvec;
>  		int		i;
> +		struct bvec_iter_all bia;
>  
>  		/*
>  		 * For the last bio, bi_private points to the ioend, so we
> @@ -150,7 +151,7 @@ xfs_destroy_ioend(
>  			next = bio->bi_private;
>  
>  		/* walk each page on bio, ending page IO on them */
> -		bio_for_each_segment_all(bvec, bio, i)
> +		bio_for_each_segment_all_sp(bvec, bio, i, bia)

It's confusing that you're splitting the old bio_for_each_segment_all
into multipage and singlepage variants, but bio_for_each_segment_all
continues to exist?

Hmm, the new multipage variant aliases the name bio_for_each_segment_all,
so clearly the _all function's sematics have changed a bit, but its name
and signature haven't, which seems likely to trip up someone who didn't
notice the behavioral change.

Is it still valid to call bio_for_each_segment_all?  I get the feeling
from this patchset that you're really supposed to decide whether you
want one page at a time or more than one page at a time and choose _sp
or _mp?

(And, seeing how this was the only patch sent to this list, the chances
are higher of someone missing out on these subtle changes...)

--D

>  			xfs_finish_page_writeback(inode, bvec, error);
>  
>  		bio_put(bio);
> -- 
> 2.9.4
> 
> --
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