linux-kernel - Re: [PATCH] bcache/md: Use raid stripe size

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Date:	Mon, 6 Jan 2014 21:04:25 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-bcache@...r.kernel.org, Neil Brown <neilb@...e.de>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] bcache/md: Use raid stripe size

On Wed, Dec 18, 2013 at 8:12 PM, Kent Overstreet <kmo@...erainc.com> wrote:
> Now that we've got code for raid5/6 stripe awareness, bcache just needs
> to know about the stripes and when writing partial stripes is expensive
> - we probably don't want to enable this optimization for raid1 or 10,
> even though they have stripes. So add a flag to queue_limits.
>
> Signed-off-by: Kent Overstreet <kmo@...erainc.com>
> ---
> This is in my pile of bcache stuff queued up for 3.14 - if no one objects it'll
> be in my bcache pull request:
>
>  drivers/md/bcache/super.c | 6 ++++++
>  drivers/md/raid5.c        | 1 +
>  include/linux/blkdev.h    | 1 +
>  3 files changed, 8 insertions(+)

Hi Kent,

> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 02cb6f0ea7..0375654adb 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -291,6 +291,7 @@ struct queue_limits {
>         unsigned char           discard_misaligned;
>         unsigned char           cluster;
>         unsigned char           discard_zeroes_data;
> +       unsigned char           raid_partial_stripes_expensive;
>  };
>
>  struct request_queue {

If you add a new member to queue_limits you need to update
blk_stack_limits() so that it propagates as you stack devices.

You probably also want to update blk_set_default_limits.

Mike
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