From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH V7 20/24] bcache: avoid to use bio_for_each_segment_all() in bch_bio_alloc_pages() To: Ming Lei 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 References: <20180627124548.3456-1-ming.lei@redhat.com> <20180627124548.3456-21-ming.lei@redhat.com> <20180628012816.GH7583@ming.t460p> From: Coly Li Message-ID: <92ae1547-39b1-472c-efbe-c0a6430fc3f6@suse.de> Date: Thu, 28 Jun 2018 10:01:39 +0800 MIME-Version: 1.0 In-Reply-To: <20180628012816.GH7583@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: On 2018/6/28 9:28 AM, Ming Lei wrote: > 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. Hi Ming, I see, thanks for the hint. Acked-by: Coly Li Coly Li