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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 70F14C32753 for ; Thu, 1 Aug 2019 22:51:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FD322084C for ; Thu, 1 Aug 2019 22:51:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733289AbfHAWu7 (ORCPT ); Thu, 1 Aug 2019 18:50:59 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:37907 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388942AbfHAWu6 (ORCPT ); Thu, 1 Aug 2019 18:50:58 -0400 Received: by mail-pg1-f193.google.com with SMTP id f5so26176064pgu.5 for ; Thu, 01 Aug 2019 15:50:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=Em7UK3RYeN+WOGI1E/PxkPUM7IdJO+sUsMzC6fv5ULA=; b=puMarA9cPTrFR4t/itHv/ugMEJtFSCh5dbO+toYNqZhDumHastLDn4OMu4+iSe62Jr 6RvwThZ8GNMsZKRTSaMAboLVRBherb2mP4kEx5CC0jVvWqBdQuoGUw8w8Bobx46evB9s 2fWqbGJ79MlJuoy0qH0aCoQg7KHQAU6gjTT2uOYVpwOYQPirNt3SLUwy+hg9bWPZr1cF TTBOG5Q0UjYXdn5zUGfl3aqx2wS/VU4zP8Wa7ecrcVVQWMYHngWnwcTl2FbGcO1v4VWM dFhNS7PYvuBdO9560XVyUfkVJN4ttBx45K9x8iKWcFLn0yGMnrgD55/bXogSUveKJpAX epIw== X-Gm-Message-State: APjAAAUzevmp91nTGrHzL1wjWD/6TCm+oKdKP3scuyYLQh4uzc0qqthb imrKywVA/FsbICVQ9NOmEiw= X-Google-Smtp-Source: APXvYqzxuKfEtD7jGxVxS+GQp3FGBazzlOHztLaVHNHDCb9RlzduLmGBS31zQZKKcxG0fL6IUdrD2Q== X-Received: by 2002:a17:90a:346c:: with SMTP id o99mr1139951pjb.20.1564699857856; Thu, 01 Aug 2019 15:50:57 -0700 (PDT) Received: from desktop-bart.svl.corp.google.com ([2620:15c:2cd:202:4308:52a3:24b6:2c60]) by smtp.gmail.com with ESMTPSA id d12sm35472010pfn.11.2019.08.01.15.50.56 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Thu, 01 Aug 2019 15:50:57 -0700 (PDT) From: Bart Van Assche To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Bart Van Assche , Ming Lei , Hannes Reinecke Subject: [PATCH v2 4/5] block: Simplify blk_bio_segment_split() Date: Thu, 1 Aug 2019 15:50:43 -0700 Message-Id: <20190801225044.143478-5-bvanassche@acm.org> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog In-Reply-To: <20190801225044.143478-1-bvanassche@acm.org> References: <20190801225044.143478-1-bvanassche@acm.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Move the max_sectors check into bvec_split_segs() such that a single call to that function can do all the necessary checks. This patch optimizes the fast path further, namely if a bvec fits in a page. Cc: Christoph Hellwig Cc: Ming Lei Cc: Hannes Reinecke Signed-off-by: Bart Van Assche --- block/blk-merge.c | 68 +++++++++++++++++++++++------------------------ 1 file changed, 33 insertions(+), 35 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index 7cea5050bbcf..a6bc08255b1b 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -157,22 +157,36 @@ static unsigned get_max_segment_size(const struct request_queue *q, queue_max_segment_size(q)); } -/* - * Split the bvec @bv into segments, and update all kinds of - * variables. +/** + * bvec_split_segs - verify whether or not a bvec should be split in the middle + * @q: [in] request queue associated with the bio associated with @bv + * @bv: [in] bvec to examine + * @nsegs: [in,out] Number of segments in the bio being built. Incremented + * by the number of segments from @bv that may be appended to that + * bio without exceeding @max_segs + * @sectors: [in,out] Number of sectors in the bio being built. Incremented + * by the number of sectors from @bv that may be appended to that + * bio without exceeding @max_sectors + * @max_segs: [in] upper bound for *@nsegs + * @max_sectors: [in] upper bound for *@sectors + * + * When splitting a bio, it can happen that a bvec is encountered that is too + * big to fit in a single segment and hence that it has to be split in the + * middle. This function verifies whether or not that should happen. The value + * %true is returned if and only if appending the entire @bv to a bio with + * *@nsegs segments and *@sectors sectors would make that bio unacceptable for + * the block driver. */ static bool bvec_split_segs(const struct request_queue *q, const struct bio_vec *bv, unsigned *nsegs, - unsigned *sectors, unsigned max_segs) + unsigned *sectors, unsigned max_segs, + unsigned max_sectors) { - unsigned len = bv->bv_len; + unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9; + unsigned len = min(bv->bv_len, max_len); unsigned total_len = 0; unsigned seg_size = 0; - /* - * Multi-page bvec may be too big to hold in one segment, so the - * current bvec has to be splitted as multiple segments. - */ while (len && *nsegs < max_segs) { seg_size = get_max_segment_size(q, bv->bv_offset + total_len); seg_size = min(seg_size, len); @@ -187,8 +201,8 @@ static bool bvec_split_segs(const struct request_queue *q, *sectors += total_len >> 9; - /* split in the middle of the bvec if len != 0 */ - return !!len; + /* tell the caller to split the bvec if it is too big to fit */ + return len > 0 || bv->bv_len > max_len; } /** @@ -229,34 +243,18 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset)) goto split; - if (sectors + (bv.bv_len >> 9) > max_sectors) { - /* - * Consider this a new segment if we're splitting in - * the middle of this vector. - */ - if (nsegs < max_segs && - sectors < max_sectors) { - /* split in the middle of bvec */ - bv.bv_len = (max_sectors - sectors) << 9; - bvec_split_segs(q, &bv, &nsegs, - §ors, max_segs); - } + if (nsegs < max_segs && + sectors + (bv.bv_len >> 9) <= max_sectors && + bv.bv_offset + bv.bv_len <= PAGE_SIZE) { + nsegs++; + sectors += bv.bv_len >> 9; + } else if (bvec_split_segs(q, &bv, &nsegs, §ors, max_segs, + max_sectors)) { goto split; } - if (nsegs == max_segs) - goto split; - bvprv = bv; bvprvp = &bvprv; - - if (bv.bv_offset + bv.bv_len <= PAGE_SIZE) { - nsegs++; - sectors += bv.bv_len >> 9; - } else if (bvec_split_segs(q, &bv, &nsegs, §ors, - max_segs)) { - goto split; - } } *segs = nsegs; @@ -363,7 +361,7 @@ unsigned int blk_recalc_rq_segments(struct request *rq) rq_for_each_bvec(bv, rq, iter) bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors, - UINT_MAX); + UINT_MAX, UINT_MAX); return nr_phys_segs; } -- 2.22.0.770.g0f2c4a37fd-goog