Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755579AbcJ2WUO (ORCPT <rfc822;w@1wt.eu>);
        Sat, 29 Oct 2016 18:20:14 -0400
Received: from mail-vk0-f66.google.com ([209.85.213.66]:35594 "EHLO
        mail-vk0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753958AbcJ2WUL (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 29 Oct 2016 18:20:11 -0400
MIME-Version: 1.0
In-Reply-To: <20161029152933.GA17241@infradead.org>
References: <1477728600-12938-1-git-send-email-tom.leiming@gmail.com>
 <1477728600-12938-24-git-send-email-tom.leiming@gmail.com> <20161029152933.GA17241@infradead.org>
From: Ming Lei <tom.leiming@gmail.com>
Date: Sun, 30 Oct 2016 06:20:09 +0800
Message-ID: <CACVXFVPVW0YJ1+X_EhHAbt1zxF6BWqgmjOM_VRdzyLTJNxJWTw@mail.gmail.com>
Subject: Re: [PATCH 23/60] block: introduce flag QUEUE_FLAG_NO_MP
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@fb.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-block <linux-block@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Christie <mchristi@redhat.com>, Hannes Reinecke <hare@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Toshi Kani <toshi.kani@hpe.com>, Shaohua Li <shli@kernel.org>,
        "open list:SOFTWARE RAID (Multiple Disks) SUPPORT" 
        <linux-raid@vger.kernel.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1212
Lines: 33

On Sat, Oct 29, 2016 at 11:29 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Sat, Oct 29, 2016 at 04:08:22PM +0800, Ming Lei wrote:
>> MD(especially raid1 and raid10) is a bit difficult to support
>> multipage bvec, so introduce this flag for not enabling multipage
>> bvec, then MD can still accept singlepage bvec only, and once
>> direct access to bvec table in MD and other fs/drivers are cleanuped,
>> the flag can be removed. BTRFS has the similar issue too.
>
> There is really no good reason for that.  The RAID1 and 10 code really
> just needs some love to use the bio cloning infrastructure, bio
> iterators and generally recent bio apis.  btrfs just needs a tiny little
> bit of help and I'll send patches soon.

That is very nice of you to do this cleanup, cool!

I guess it still need a bit time, and hope that won't be the block
for the whole patchset, :-)

[linux-2.6-next]$git grep -n -E "bi_io_vec|bi_vcnt" ./fs/btrfs/ | wc -l
45

[linux-2.6-next]$git grep -n -E "bi_io_vec|bi_vcnt" ./drivers/md/ |
grep raid | wc -l
54

>
> Having two different code path is just asking for trouble in the long
> run.

Definitely, that flag is introduced just as a short-term solution.

Thanks,
Ming Lei