Re: [PATCH 23/60] block: introduce flag QUEUE_FLAG_NO_MP

[Ming Lei]

On Sat, Oct 29, 2016 at 11:29 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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