[[NOTE to dm-devel people - one of the patches here remove some
 now-unused code from dm-raid.c plus a declaration from device-mapper.h ]]]


On Mon, 18 Apr 2011 10:10:18 +0200 Jens Axboe [off-list ref] wrote:

On 2011-04-18 09:25, NeilBrown wrote:

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Therefore md cannot put anything useful on the list in 'struct blk_plug'.

That is the heart of the problem.

Hmm, I don't really see a way to avoid the list in that case. You really
do need some way to queue items, a single callback or flag or pointer
will not suffice.

I've added the patch and removed the (now) useless ->unplugged_fn
callback. I suggest you base your md changes on top of my for-linus
branch and tell me when you are confident it looks good, then I'll pull
in your MD changes and submit them later today.

OK with you?

Yes, that's perfect.  Thanks.

All of my plugging-related patches are now in a 'for-jens' branch:

The following changes since commit 99e22598e9a8e0a996d69c8c0f6b7027cb57720a:

  block: drop queue lock before calling __blk_run_queue() for kblockd punt (2011-04-18 09:59:55 +0200)

are available in the git repository at:
  git://neil.brown.name/md for-jens

NeilBrown (6):
      md: use new plugging interface for RAID IO.
      md/dm - remove remains of plug_fn callback.
      md - remove old plugging code.
      md: provide generic support for handling unplug callbacks.
      md: incorporate new plugging into raid5.
      md: fix up raid1/raid10 unplugging.

 drivers/md/dm-raid.c          |    8 ----
 drivers/md/md.c               |   87 +++++++++++++++++++++-------------------
 drivers/md/md.h               |   26 ++----------
 drivers/md/raid1.c            |   29 +++++++-------
 drivers/md/raid10.c           |   27 ++++++-------
 drivers/md/raid5.c            |   61 ++++++++++++----------------
 drivers/md/raid5.h            |    2 -
 include/linux/device-mapper.h |    1 -
 8 files changed, 103 insertions(+), 138 deletions(-)


Thanks,
NeilBrown