From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9EB70C433E1 for ; Mon, 17 Aug 2020 06:26:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8044520772 for ; Mon, 17 Aug 2020 06:26:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726596AbgHQG0h (ORCPT ); Mon, 17 Aug 2020 02:26:37 -0400 Received: from verein.lst.de ([213.95.11.211]:55179 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726451AbgHQG0h (ORCPT ); Mon, 17 Aug 2020 02:26:37 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 9A73468B05; Mon, 17 Aug 2020 08:26:34 +0200 (CEST) Date: Mon, 17 Aug 2020 08:26:34 +0200 From: Christoph Hellwig To: Baolin Wang Cc: axboe@kernel.dk, ming.lei@redhat.com, hch@lst.de, baolin.wang7@gmail.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND 3/5] block: Add a new helper to attempt to merge a bio Message-ID: <20200817062634.GC12248@lst.de> References: <5b932aa51fc2b46c381d7b83d591a6ddbf05b199.1597637287.git.baolin.wang@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5b932aa51fc2b46c381d7b83d591a6ddbf05b199.1597637287.git.baolin.wang@linux.alibaba.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Aug 17, 2020 at 12:09:17PM +0800, Baolin Wang wrote: > There are lots of duplicated code when trying to merge a bio from > plug list and sw queue, we can introduce a new helper to attempt > to merge a bio, which can simplify the blk_mq_bio_list_merge() > and blk_attempt_plug_merge(). Looks sensible, but two comments: > +enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q, > + struct request *rq, > + struct bio *bio, > + unsigned int nr_segs) > +{ > + bool merged = false; > + > + if (!blk_rq_merge_ok(rq, bio)) > + return BIO_MERGE_NONE; > + > + switch (blk_try_merge(rq, bio)) { > + case ELEVATOR_BACK_MERGE: > + merged = bio_attempt_back_merge(rq, bio, nr_segs); > + break; > + case ELEVATOR_FRONT_MERGE: > + merged = bio_attempt_front_merge(rq, bio, nr_segs); > + break; > + case ELEVATOR_DISCARD_MERGE: > + merged = bio_attempt_discard_merge(q, rq, bio); > + break; Can't we also switch the bio_attempt_*merge helpers to return enum bio_merge_status to simplify this a bit? Also I think these helpers can be marked static now, although I didn't actually apply your series, so I might have missed something. > +++ b/block/blk-mq-sched.c > @@ -391,31 +391,17 @@ bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list, > { > struct request *rq; > int checked = 8; > + enum bio_merge_status merge; > > list_for_each_entry_reverse(rq, list, queuelist) { > - bool merged = false; > - > if (!checked--) > break; > > + merge = blk_attempt_bio_merge(q, rq, bio, nr_segs); > + if (merge == BIO_MERGE_NONE) > continue; > > + return merge == BIO_MERGE_OK ? true: false; Maybe write this a little more explicit: switch (blk_attempt_bio_merge(q, rq, bio, nr_segs)) { case BIO_MERGE_NONE: continue: case BIO_MERGE_OK: return true; case BIO_MERGE_FAILED: return false; } > enum elv_merge blk_try_merge(struct request *rq, struct bio *bio); > > +enum bio_merge_status { > + BIO_MERGE_OK, > + BIO_MERGE_NONE, > + BIO_MERGE_FAILED, > +}; > + > +enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q, > + struct request *rq, struct bio *bio, unsigned int nr_segs); > + > int blk_dev_init(void); > > /* > -- > 1.8.3.1 ---end quoted text---