From patchwork Thu Sep 21 17:29:09 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "jianchao.wang" X-Patchwork-Id: 9963169 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 7D12A6056A for ; Thu, 21 Sep 2017 01:30:37 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 714362906A for ; Thu, 21 Sep 2017 01:30:37 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 65C0F29074; Thu, 21 Sep 2017 01:30:37 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.7 required=2.0 tests=BAYES_00, DATE_IN_FUTURE_12_24, RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 0DEEE2907A for ; Thu, 21 Sep 2017 01:30:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751499AbdIUBaY (ORCPT ); Wed, 20 Sep 2017 21:30:24 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:25350 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751095AbdIUBaX (ORCPT ); Wed, 20 Sep 2017 21:30:23 -0400 Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by aserp1040.oracle.com (Sentrion-MTA-4.3.2/Sentrion-MTA-4.3.2) with ESMTP id v8L1TuFd004425 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 21 Sep 2017 01:29:57 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id v8L1TtgY026332 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 21 Sep 2017 01:29:56 GMT Received: from abhmp0001.oracle.com (abhmp0001.oracle.com [141.146.116.7]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id v8L1TqWv009402; Thu, 21 Sep 2017 01:29:54 GMT Received: from will-ThinkCentre-M910s.cn.oracle.com (/10.182.71.22) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 20 Sep 2017 18:29:47 -0700 From: Jianchao Wang To: Jens Axboe , hch@infradead.org Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Jianchao Wang Subject: [V2] block: consider merge of segments when merge bio into rq Date: Fri, 22 Sep 2017 01:29:09 +0800 Message-Id: <1506014949-24184-1-git-send-email-jianchao.w.wang@oracle.com> X-Mailer: git-send-email 2.7.4 X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When account the nr_phys_segments during merging bios into rq, only consider segments merging in individual bio but not all the bios in a rq. This leads to the bigger nr_phys_segments of rq than the real one when the segments of bios in rq are contiguous and mergeable. The nr_phys_segments of rq will exceed max_segmets of q and stop merging while the sectors of rq maybe far away from the max_sectors of q. In practice, the merging will stop due to max_segmets limit while the segments in the rq are contiguous and mergeable during the mkfs.ext4 workload on my local. This could be harmful to the performance of sequential operations. To fix it, consider the segments merge when account nr_phys_segments of rq during merging bio into rq. Decrease the nr_phys_segments of rq by 1 when the adjacent segments in bio and rq are contiguous and mergeable. Consequently get more fully merging and better performance in sequential operations. In addition, it could eliminate the wasting of scatterlist structure. On my local mkfs.ext4 workload, the final size of rq issued raise from 168 sectors (max_segmets is 168) to 2560 sectors (max_sector_kb is 1280). V2 : Add more comment to elaborate how this issue found and result after apply the patch. Signed-off-by: Jianchao Wang --- block/blk-merge.c | 98 ++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 64 insertions(+), 34 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index 14b6e37..b2f54fd 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -472,54 +472,60 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq, } EXPORT_SYMBOL(blk_rq_map_sg); -static inline int ll_new_hw_segment(struct request_queue *q, - struct request *req, - struct bio *bio) -{ - int nr_phys_segs = bio_phys_segments(q, bio); - - if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q)) - goto no_merge; - - if (blk_integrity_merge_bio(q, req, bio) == false) - goto no_merge; - - /* - * This will form the start of a new hw segment. Bump both - * counters. - */ - req->nr_phys_segments += nr_phys_segs; - return 1; - -no_merge: - req_set_nomerge(q, req); - return 0; -} - int ll_back_merge_fn(struct request_queue *q, struct request *req, struct bio *bio) { + unsigned int seg_size; + int total_nr_phys_segs; + bool contig; + if (req_gap_back_merge(req, bio)) return 0; if (blk_integrity_rq(req) && integrity_req_gap_back_merge(req, bio)) return 0; if (blk_rq_sectors(req) + bio_sectors(bio) > - blk_rq_get_max_sectors(req, blk_rq_pos(req))) { - req_set_nomerge(q, req); - return 0; - } + blk_rq_get_max_sectors(req, blk_rq_pos(req))) + goto no_merge; + if (!bio_flagged(req->biotail, BIO_SEG_VALID)) blk_recount_segments(q, req->biotail); if (!bio_flagged(bio, BIO_SEG_VALID)) blk_recount_segments(q, bio); - return ll_new_hw_segment(q, req, bio); + if (blk_integrity_merge_bio(q, req, bio) == false) + goto no_merge; + + seg_size = req->biotail->bi_seg_back_size + bio->bi_seg_front_size; + total_nr_phys_segs = req->nr_phys_segments + bio_phys_segments(q, bio); + + contig = blk_phys_contig_segment(q, req->biotail, bio); + if (contig) + total_nr_phys_segs--; + + if (unlikely(total_nr_phys_segs > queue_max_segments(q))) + goto no_merge; + + if (contig) { + if (req->nr_phys_segments == 1) + req->bio->bi_seg_front_size = seg_size; + if (bio->bi_phys_segments == 1) + bio->bi_seg_back_size = seg_size; + } + req->nr_phys_segments = total_nr_phys_segs; + return 1; + +no_merge: + req_set_nomerge(q, req); + return 0; } int ll_front_merge_fn(struct request_queue *q, struct request *req, struct bio *bio) { + unsigned int seg_size; + int total_nr_phys_segs; + bool contig; if (req_gap_front_merge(req, bio)) return 0; @@ -527,16 +533,40 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req, integrity_req_gap_front_merge(req, bio)) return 0; if (blk_rq_sectors(req) + bio_sectors(bio) > - blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) { - req_set_nomerge(q, req); - return 0; - } + blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) + goto no_merge; + if (!bio_flagged(bio, BIO_SEG_VALID)) blk_recount_segments(q, bio); if (!bio_flagged(req->bio, BIO_SEG_VALID)) blk_recount_segments(q, req->bio); - return ll_new_hw_segment(q, req, bio); + if (blk_integrity_merge_bio(q, req, bio) == false) + goto no_merge; + + seg_size = req->bio->bi_seg_front_size + bio->bi_seg_back_size; + total_nr_phys_segs = req->nr_phys_segments + bio_phys_segments(q, bio); + + contig = blk_phys_contig_segment(q, bio, req->bio); + if (contig) + total_nr_phys_segs--; + + if (unlikely(total_nr_phys_segs > queue_max_segments(q))) + goto no_merge; + + if (contig) { + if (req->nr_phys_segments == 1) + req->biotail->bi_seg_back_size = seg_size; + if (bio->bi_phys_segments == 1) + bio->bi_seg_front_size = seg_size; + } + + req->nr_phys_segments = total_nr_phys_segs; + return 1; + +no_merge: + req_set_nomerge(q, req); + return 0; } /*