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

Ming Lei
2018-11-19T08:46:01Z

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@redhat.com>
> > Cc: Kent Overstreet <kent.overstreet@gmail.com>
> > Cc: Mike Snitzer <snitzer@redhat.com>
> > Cc: dm-devel@redhat.com
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: linux-fsdevel@vger.kernel.org
> > Cc: Shaohua Li <shli@kernel.org>
> > Cc: linux-raid@vger.kernel.org
> > Cc: linux-erofs@lists.ozlabs.org
> > Cc: David Sterba <dsterba@suse.com>
> > Cc: linux-btrfs@vger.kernel.org
> > Cc: Darrick J. Wong <darrick.wong@oracle.com>
> > Cc: linux-xfs@vger.kernel.org
> > Cc: Gao Xiang <gaoxiang25@huawei.com>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Theodore Ts'o <tytso@mit.edu>
> > Cc: linux-ext4@vger.kernel.org
> > Cc: Coly Li <colyli@suse.de>
> > Cc: linux-bcache@vger.kernel.org
> > Cc: Boaz Harrosh <ooo@electrozaur.com>
> > Cc: Bob Peterson <rpeterso@redhat.com>
> > Cc: cluster-devel@redhat.com
> > Signed-off-by: Ming Lei <ming.lei@redhat.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?

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