linux-kernel - Re: [PATCH 26/60] btrfs: set NO_MP for request queues behind BTRFS

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Message-ID: <20161031175828.GB48277@clm-mbp.thefacebook.com>
Date:   Mon, 31 Oct 2016 11:58:29 -0600
From:   Chris Mason <clm@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Ming Lei <tom.leiming@...il.com>, Jens Axboe <axboe@...com>,
        <linux-kernel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.com>,
        "open list:BTRFS FILE SYSTEM" <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH 26/60] btrfs: set NO_MP for request queues behind BTRFS

On Mon, Oct 31, 2016 at 08:36:44AM -0700, Christoph Hellwig wrote:
>On Sat, Oct 29, 2016 at 04:08:25PM +0800, Ming Lei wrote:
>> There are lots of direct access to .bi_vcnt & .bi_io_vec
>> of bio, and it isn't ready to support multipage bvecs
>> for BTRFS, so set NO_MP for these request queues.
>
>For one bio is an I/O submitter, it has absolutely no business changing
>queue flags - if we need to stick to this limitation it simply needs
>a version of bio_add_page that doesn't create multi-page bvecs.
>
>Second I don't think making it multipage bvec aware is all that hard,
>and we should aim for doing the proper thing.

Yeah, I'd rather make us less special.  The direct access was a short 
term fix to adjust to the new bio interfaces, we should clean it up.

-chris