linux-ext4 - Re: [PATCH V10 14/19] block: enable multipage bvecs

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Date:   Thu, 15 Nov 2018 17:56:27 -0800
From:   Omar Sandoval <osandov@...ndov.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Christoph Hellwig <hch@....de>, Theodore Ts'o <tytso@....edu>,
        linux-ext4@...r.kernel.org, Coly Li <colyli@...e.de>,
        linux-bcache@...r.kernel.org, Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V10 14/19] block: enable multipage bvecs

On Thu, Nov 15, 2018 at 04:53:01PM +0800, Ming Lei wrote:
> This patch pulls the trigger for multi-page bvecs.
> 
> Now any request queue which supports queue cluster will see multi-page
> bvecs.
> 
> Cc: Dave Chinner <dchinner@...hat.com>
> Cc: Kent Overstreet <kent.overstreet@...il.com>
> Cc: Mike Snitzer <snitzer@...hat.com>
> Cc: dm-devel@...hat.com
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: Shaohua Li <shli@...nel.org>
> Cc: linux-raid@...r.kernel.org
> Cc: linux-erofs@...ts.ozlabs.org
> Cc: David Sterba <dsterba@...e.com>
> Cc: linux-btrfs@...r.kernel.org
> Cc: Darrick J. Wong <darrick.wong@...cle.com>
> Cc: linux-xfs@...r.kernel.org
> Cc: Gao Xiang <gaoxiang25@...wei.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Theodore Ts'o <tytso@....edu>
> Cc: linux-ext4@...r.kernel.org
> Cc: Coly Li <colyli@...e.de>
> Cc: linux-bcache@...r.kernel.org
> Cc: Boaz Harrosh <ooo@...ctrozaur.com>
> Cc: Bob Peterson <rpeterso@...hat.com>
> Cc: cluster-devel@...hat.com
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>  block/bio.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 6486722d4d4b..ed6df6f8e63d 100644
> --- a/block/bio.c
> +++ b/block/bio.c

This comment above __bio_try_merge_page() doesn't make sense after this
change:

 This is a
 a useful optimisation for file systems with a block size smaller than the
 page size.

Can you please get rid of it in this patch?

> @@ -767,12 +767,24 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
>  
>  	if (bio->bi_vcnt > 0) {
>  		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> -
> -		if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
> -			bv->bv_len += len;
> -			bio->bi_iter.bi_size += len;
> -			return true;
> -		}
> +		struct request_queue *q = NULL;
> +
> +		if (page == bv->bv_page && off == (bv->bv_offset + bv->bv_len)
> +				&& (off + len) <= PAGE_SIZE)
> +			goto merge;

The parentheses around (bv->bv_offset + bv->bv_len) and (off + len) are
unnecessary noise.

What's the point of the new (off + len) <= PAGE_SIZE check?

> +
> +		if (bio->bi_disk)
> +			q = bio->bi_disk->queue;
> +
> +		/* disable multi-page bvec too if cluster isn't enabled */
> +		if (!q || !blk_queue_cluster(q) ||
> +		    ((page_to_phys(bv->bv_page) + bv->bv_offset + bv->bv_len) !=
> +		     (page_to_phys(page) + off)))

More unnecessary parentheses here.

> +			return false;
> + merge:
> +		bv->bv_len += len;
> +		bio->bi_iter.bi_size += len;
> +		return true;
>  	}
>  	return false;
>  }
> -- 
> 2.9.5
>