linux-kernel - Re: [PATCH V6 11/30] block: implement bio_pages_all() via bio_for_each_segment

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Message-ID: <20180614062022.GB3336@infradead.org>
Date:   Wed, 13 Jun 2018 23:20:22 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kent Overstreet <kent.overstreet@...il.com>,
        David Sterba <dsterba@...e.cz>,
        Huang Ying <ying.huang@...el.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Theodore Ts'o <tytso@....edu>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Coly Li <colyli@...e.de>, Filipe Manana <fdmanana@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH V6 11/30] block: implement bio_pages_all() via
 bio_for_each_segment_all()

On Thu, Jun 14, 2018 at 09:23:54AM +0800, Ming Lei wrote:
> On Wed, Jun 13, 2018 at 07:44:12AM -0700, Christoph Hellwig wrote:
> > Given that we have a single, dubious user of bio_pages_all I'd rather
> > see it as an opencoded bio_for_each_ loop in the caller.
> 
> Yeah, that is fine since there is only one user in btrfs.

And I suspect it really is checking for the wrong thing.  I don't
fully understand that code, but as far as I can tell it really
needs to know if there is more than a file system block of data in
the bio, and btrfs conflats pages with blocks.  But I'd need btrfs
folks to confirm this.