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

[Ming Lei]

On Thu, Nov 15, 2018 at 05:56:27PM -0800, Omar Sandoval wrote:
> 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@xxxxxxxxxx>
> > Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> > Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> > Cc: dm-devel@xxxxxxxxxx
> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> > Cc: Shaohua Li <shli@xxxxxxxxxx>
> > Cc: linux-raid@xxxxxxxxxxxxxxx
> > Cc: linux-erofs@xxxxxxxxxxxxxxxx
> > Cc: David Sterba <dsterba@xxxxxxxx>
> > Cc: linux-btrfs@xxxxxxxxxxxxxxx
> > Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > Cc: linux-xfs@xxxxxxxxxxxxxxx
> > Cc: Gao Xiang <gaoxiang25@xxxxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Theodore Ts'o <tytso@xxxxxxx>
> > Cc: linux-ext4@xxxxxxxxxxxxxxx
> > Cc: Coly Li <colyli@xxxxxxx>
> > Cc: linux-bcache@xxxxxxxxxxxxxxx
> > Cc: Boaz Harrosh <ooo@xxxxxxxxxxxxxxx>
> > Cc: Bob Peterson <rpeterso@xxxxxxxxxx>
> > Cc: cluster-devel@xxxxxxxxxx
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> >  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?

I understand __bio_try_merge_page() still works for original cases, so
looks the optimization for sub-pagesize is still there too, isn't it?

> 
> > @@ -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?

Yeah, I don't know why I did it, :-(, the check is absolutely always true.

> 
> > +
> > +		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.

OK.

Thanks,
Ming