[Drbd-dev] RFC: always use REQ_OP_WRITE_ZEROES for zeroing offload

[Christoph Hellwig]

On Mon, Mar 27, 2017 at 10:03:07AM -0400, Mike Snitzer wrote:
> By "you" I assume you're referring to Lars?

Yes.

> Lars' approach for discard,
> when drbd is layered on dm-thinp, feels over-engineered.  Not his fault,
> the way discard and zeroing got conflated certainly lends itself to
> these ugly hacks.  SO I do appreciate that for anything to leverage
> discard_zeroes_data it needs to be reliable.  Which runs counter to how
> discard was implemented (discard may get silently dropped!)  But that is
> why dm-thinp doesn't advertise dzd.  Anyway...

That's exactly what this series does - remove discard_zeroes_data and
use the new REQ_OP_WRITE_ZEROES for anything that wants zeroing offload.

> As for the blkdev_issue_zeroout() resorting to manually zeroing the
> range, if the discard fails or dzd not supported, that certainly
> requires DM thinp to implement manual zeroing of the head and tail of
> the range if partial blocks are being zeroed.  So I welcome any advances
> there.  It is probably something that is best left to Joe or myself to
> tackle.  But I'll gladly accept patches ;)

Ok, I'll happily leave this to the two of you..