Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755371AbcL0QCt (ORCPT ); Tue, 27 Dec 2016 11:02:49 -0500 Received: from mail-pg0-f66.google.com ([74.125.83.66]:33823 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755742AbcL0QB3 (ORCPT ); Tue, 27 Dec 2016 11:01:29 -0500 From: Ming Lei To: Jens Axboe , linux-kernel@vger.kernel.org Cc: linux-block@vger.kernel.org, Christoph Hellwig , Ming Lei , Jens Axboe Subject: [PATCH v1 25/54] block: blk-merge: try to make front segments in full size Date: Tue, 27 Dec 2016 23:56:14 +0800 Message-Id: <1482854250-13481-26-git-send-email-tom.leiming@gmail.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1482854250-13481-1-git-send-email-tom.leiming@gmail.com> References: <1482854250-13481-1-git-send-email-tom.leiming@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3524 Lines: 124 When merging one bvec into segment, if the bvec is too big to merge, current policy is to move the whole bvec into another new segment. This patchset changes the policy into trying to maximize size of front segments, that means in above situation, part of bvec is merged into current segment, and the remainder is put into next segment. This patch prepares for support multipage bvec because it can be quite common to see this case and we should try to make front segments in full size. Signed-off-by: Ming Lei --- block/blk-merge.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 49 insertions(+), 5 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index e3abc835e4b7..a801f62a104b 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -95,6 +95,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, struct bio *new = NULL; const unsigned max_sectors = get_max_io_size(q, bio); unsigned bvecs = 0; + unsigned advance = 0; bio_for_each_segment(bv, bio, iter) { /* @@ -141,12 +142,32 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, } if (bvprvp && blk_queue_cluster(q)) { - if (seg_size + bv.bv_len > queue_max_segment_size(q)) - goto new_segment; if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv)) goto new_segment; if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv)) goto new_segment; + if (seg_size + bv.bv_len > queue_max_segment_size(q)) { + /* + * On assumption is that initial value of + * @seg_size(equals to bv.bv_len) won't be + * bigger than max segment size, but will + * becomes false after multipage bvec comes. + */ + advance = queue_max_segment_size(q) - seg_size; + + if (advance > 0) { + seg_size += advance; + sectors += advance >> 9; + bv.bv_len -= advance; + bv.bv_offset += advance; + } + + /* + * Still need to put remainder of current + * bvec into a new segment. + */ + goto new_segment; + } seg_size += bv.bv_len; bvprv = bv; @@ -168,6 +189,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, seg_size = bv.bv_len; sectors += bv.bv_len >> 9; + /* restore the bvec for iterator */ + if (advance) { + bv.bv_len += advance; + bv.bv_offset -= advance; + advance = 0; + } } do_split = false; @@ -370,16 +397,29 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec, { int nbytes = bvec->bv_len; + unsigned advance = 0; if (*sg && *cluster) { - if ((*sg)->length + nbytes > queue_max_segment_size(q)) - goto new_segment; - if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) goto new_segment; if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) goto new_segment; + /* + * try best to merge part of the bvec into previous + * segment and follow same policy with + * blk_bio_segment_split() + */ + if ((*sg)->length + nbytes > queue_max_segment_size(q)) { + advance = queue_max_segment_size(q) - (*sg)->length; + if (advance) { + (*sg)->length += advance; + bvec->bv_offset += advance; + bvec->bv_len -= advance; + } + goto new_segment; + } + (*sg)->length += nbytes; } else { new_segment: @@ -402,6 +442,10 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec, sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset); (*nsegs)++; + + /* for making iterator happy */ + bvec->bv_offset -= advance; + bvec->bv_len += advance; } *bvprv = *bvec; } -- 2.7.4