On Mon, Jan 06, 2014 at 09:04:25PM -0500, Mike Snitzer wrote:

On Wed, Dec 18, 2013 at 8:12 PM, Kent Overstreet [off-list ref] wrote:

quoted

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 <redacted>
---
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,

quoted

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.

Thanks, going to send Jens a new pull after he does some merging so I'll include
that in the updated version.