On Tue, Aug 17 2010 at 12:51pm -0400,
Tejun Heo [off-list ref] wrote:

Hello,

On 08/17/2010 04:07 PM, Mike Snitzer wrote:

quoted

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With the patch applied, there's no second flush.  Those requests would
now be REQ_FLUSH + REQ_DISCARD.  The first can't be avoided anyway and
there won't be the second flush to begin with, so I don't think this
worsens anything.

Makes sense, but your patches still need to be refreshed against the
latest (2.6.36-rc1) upstream code.  Numerous changes went in to DM
recently.

Sure thing.  The block part isn't fixed yet and so the RFC tag.  Once
the block layer part is settled, it probably should be pulled into
dm/md and other trees and conversions should happen there.

Why base your work on a partial 2.6.36 tree?  Why not rebase to linus'
2.6.36-rc1?

Once we get the changes in a more suitable state (across the entire
tree) we can split the individual changes out to their respective
trees.  Without a comprehensive tree I fear this code isn't going to get
tested or reviewed properly.

For example: any review of DM changes, against stale DM code, is wasted
effort.

quoted

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* For request based dm:

  * The sequencing is done by the block layer for the top level
    request_queue, so the only things request based dm needs to make
    sure is 1. handling empty REQ_FLUSH correctly (block layer will
    only send down empty REQ_FLUSHes) and 2. propagate REQ_FUA bit to
    member devices.

OK, so seems 1 is done, 2 is still TODO.  Looking at your tree it seems
2 would be as simple as using the following in

Oh, I was talking about the other way around.  Passing REQ_FUA in
bio->bi_rw down to member request_queues.  Sometimes while
constructing clone / split bios, the bit is lost (e.g. md raid5).

Seems we need to change __blk_rq_prep_clone to propagate REQ_FUA just
like REQ_DISCARD: http://git.kernel.org/linus/3383977

Doesn't seem like we need to do the same for REQ_FLUSH (at least not for
rq-based DM's benefit) because dm.c:setup_clone already special cases
flush requests and sets REQ_FLUSH in cmd_flags.

Mike