From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 28 Jun 2018 09:28:18 +0800 From: Ming Lei To: Coly Li Cc: Jens Axboe , Christoph Hellwig , Kent Overstreet , David Sterba , Huang Ying , Mike Snitzer , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Theodore Ts'o , "Darrick J . Wong" , Filipe Manana , Randy Dunlap , linux-bcache@vger.kernel.org Subject: Re: [PATCH V7 20/24] bcache: avoid to use bio_for_each_segment_all() in bch_bio_alloc_pages() Message-ID: <20180628012816.GH7583@ming.t460p> References: <20180627124548.3456-1-ming.lei@redhat.com> <20180627124548.3456-21-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: On Wed, Jun 27, 2018 at 11:55:33PM +0800, Coly Li wrote: > On 2018/6/27 8:45 PM, Ming Lei wrote: > > bch_bio_alloc_pages() is always called on one new bio, so it is safe > > to access the bvec table directly. Given it is the only kind of this > > case, open code the bvec table access since bio_for_each_segment_all() > > will be changed to support for iterating over multipage bvec. > > > > Cc: Coly Li > > Cc: linux-bcache@vger.kernel.org > > Signed-off-by: Ming Lei > > --- > > drivers/md/bcache/util.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c > > index fc479b026d6d..9f2a6fd5dfc9 100644 > > --- a/drivers/md/bcache/util.c > > +++ b/drivers/md/bcache/util.c > > @@ -268,7 +268,7 @@ int bch_bio_alloc_pages(struct bio *bio, gfp_t gfp_mask) > > int i; > > struct bio_vec *bv; > > > > Hi Ming, > > > - bio_for_each_segment_all(bv, bio, i) { > > + for (i = 0, bv = bio->bi_io_vec; i < bio->bi_vcnt; bv++) { > > > Is it possible to treat this as a special condition of > bio_for_each_segement_all() ? I mean only iterate one time in > bvec_for_each_segment(). I hope the above change is not our last choice > before I reply an Acked-by :-) Now the bvec from bio_for_each_segement_all() can't be changed any more since the referenced 'bvec' is generated in-flight given we store real multipage bvec. BTW, this way is actually suggested by Christoph for saving one new helper of bio_for_each_bvec_all() as done in V6, and per previous discussion, seems both Kent and Christoph agrees to convert bcache into bio_add_page() finally. So I guess this open code style should be fine. Thanks, Ming