Return-Path: Received: from mail-pf1-f196.google.com ([209.85.210.196]:46598 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726511AbeK0JKY (ORCPT ); Tue, 27 Nov 2018 04:10:24 -0500 Received: by mail-pf1-f196.google.com with SMTP id c73so7248960pfe.13 for ; Mon, 26 Nov 2018 14:14:49 -0800 (PST) Date: Mon, 26 Nov 2018 14:14:47 -0800 From: Omar Sandoval To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Theodore Ts'o , Omar Sandoval , Sagi Grimberg , Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , Christoph Hellwig , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com Subject: Re: [PATCH V12 04/20] block: don't use bio->bi_vcnt to figure out segment number Message-ID: <20181126221447.GE30411@vader> References: <20181126021720.19471-1-ming.lei@redhat.com> <20181126021720.19471-5-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181126021720.19471-5-ming.lei@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Nov 26, 2018 at 10:17:04AM +0800, Ming Lei wrote: > It is wrong to use bio->bi_vcnt to figure out how many segments > there are in the bio even though CLONED flag isn't set on this bio, > because this bio may be splitted or advanced. > > So always use bio_segments() in blk_recount_segments(), and it shouldn't > cause any performance loss now because the physical segment number is figured > out in blk_queue_split() and BIO_SEG_VALID is set meantime since > bdced438acd83ad83a6c ("block: setup bi_phys_segments after splitting"). > > Reviewed-by: Christoph Hellwig Reviewed-by: Omar Sandoval > Fixes: 76d8137a3113 ("blk-merge: recaculate segment if it isn't less than max segments") > Signed-off-by: Ming Lei > --- > block/blk-merge.c | 8 +------- > 1 file changed, 1 insertion(+), 7 deletions(-) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index e69d8f8ba819..51ec6ca56a0a 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -367,13 +367,7 @@ void blk_recalc_rq_segments(struct request *rq) > > void blk_recount_segments(struct request_queue *q, struct bio *bio) > { > - unsigned short seg_cnt; > - > - /* estimate segment number by bi_vcnt for non-cloned bio */ > - if (bio_flagged(bio, BIO_CLONED)) > - seg_cnt = bio_segments(bio); > - else > - seg_cnt = bio->bi_vcnt; > + unsigned short seg_cnt = bio_segments(bio); > > if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) && > (seg_cnt < queue_max_segments(q))) > -- > 2.9.5 >