Return-Path: Received: from mail-pl1-f196.google.com ([209.85.214.196]:43603 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726271AbeKPI2a (ORCPT ); Fri, 16 Nov 2018 03:28:30 -0500 Received: by mail-pl1-f196.google.com with SMTP id g59-v6so10119219plb.10 for ; Thu, 15 Nov 2018 14:18:50 -0800 (PST) Date: Thu, 15 Nov 2018 14:18:47 -0800 From: Omar Sandoval To: Mike Snitzer Cc: Ming Lei , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Kent Overstreet , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, linux-erofs@lists.ozlabs.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , Christoph Hellwig , Theodore Ts'o , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com Subject: Re: [PATCH V10 03/19] block: use bio_for_each_bvec() to compute multi-page bvec count Message-ID: <20181115221847.GD9348@vader> References: <20181115085306.9910-1-ming.lei@redhat.com> <20181115085306.9910-4-ming.lei@redhat.com> <20181115202028.GC9348@vader> <20181115210510.GA24908@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181115210510.GA24908@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Nov 15, 2018 at 04:05:10PM -0500, Mike Snitzer wrote: > On Thu, Nov 15 2018 at 3:20pm -0500, > Omar Sandoval wrote: > > > On Thu, Nov 15, 2018 at 04:52:50PM +0800, Ming Lei wrote: > > > First it is more efficient to use bio_for_each_bvec() in both > > > blk_bio_segment_split() and __blk_recalc_rq_segments() to compute how > > > many multi-page bvecs there are in the bio. > > > > > > Secondly once bio_for_each_bvec() is used, the bvec may need to be > > > splitted because its length can be very longer than max segment size, > > > so we have to split the big bvec into several segments. > > > > > > Thirdly when splitting multi-page bvec into segments, the max segment > > > limit may be reached, so the bio split need to be considered under > > > this situation too. > > > > > > Cc: Dave Chinner > > > Cc: Kent Overstreet > > > Cc: Mike Snitzer > > > Cc: dm-devel@redhat.com > > > Cc: Alexander Viro > > > Cc: linux-fsdevel@vger.kernel.org > > > Cc: Shaohua Li > > > Cc: linux-raid@vger.kernel.org > > > Cc: linux-erofs@lists.ozlabs.org > > > Cc: David Sterba > > > Cc: linux-btrfs@vger.kernel.org > > > Cc: Darrick J. Wong > > > Cc: linux-xfs@vger.kernel.org > > > Cc: Gao Xiang > > > Cc: Christoph Hellwig > > > Cc: Theodore Ts'o > > > Cc: linux-ext4@vger.kernel.org > > > Cc: Coly Li > > > Cc: linux-bcache@vger.kernel.org > > > Cc: Boaz Harrosh > > > Cc: Bob Peterson > > > Cc: cluster-devel@redhat.com > > > Signed-off-by: Ming Lei > > > --- > > > block/blk-merge.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++--------- > > > 1 file changed, 76 insertions(+), 14 deletions(-) > > > > > > diff --git a/block/blk-merge.c b/block/blk-merge.c > > > index 91b2af332a84..6f7deb94a23f 100644 > > > --- a/block/blk-merge.c > > > +++ b/block/blk-merge.c > > > @@ -160,6 +160,62 @@ static inline unsigned get_max_io_size(struct request_queue *q, > > > return sectors; > > > } > > > > > > +/* > > > + * Split the bvec @bv into segments, and update all kinds of > > > + * variables. > > > + */ > > > +static bool bvec_split_segs(struct request_queue *q, struct bio_vec *bv, > > > + unsigned *nsegs, unsigned *last_seg_size, > > > + unsigned *front_seg_size, unsigned *sectors) > > > +{ > > > + bool need_split = false; > > > + unsigned len = bv->bv_len; > > > + unsigned total_len = 0; > > > + unsigned new_nsegs = 0, seg_size = 0; > > > > "unsigned int" here and everywhere else. > > Curious why? I've wondered what govens use of "unsigned" vs "unsigned > int" recently and haven't found _the_ reason to pick one over the other. My only reason to prefer unsigned int is consistency. unsigned int is much more common in the kernel: $ ag --cc -s 'unsigned\s+int' | wc -l 129632 $ ag --cc -s 'unsigned\s+(?!char|short|int|long)' | wc -l 22435 checkpatch also warns on plain unsigned.