[PATCH RFC] nvme: rewrite discard support

[Ming Lin]

On Thu, 2016-03-17 at 15:33 +0000, Keith Busch wrote:
> On Wed, Mar 16, 2016 at 04:15:32PM -0700, Ming Lin wrote:
> > From: Ming Lin <ming.l at ssi.samsung.com>
> > 
> > This rewrites nvme_setup_discard() similar as sd_setup_discard_cmnd().
> > And moves it to common code so fabrics driver can also use it.
> 
> Initial thoughts on this, I see the appeal to having a generic NVMe
> discard setup, but I liked the existing implementation not needing a
> special case for discard check on every IO in the completion handler.
> 
> Allocating a page for just 16 bytes of data seems a bit wasteful even
> if it is short-lived. When it was allocating 256b from the DMA pool,
> the smaller amount of additional data seemed worth it for not creating
> a conditional completion.

How about moving the prp_small_pool to the core(and rename it to
nvme_small_pool)?

Then DISCARD can also use this pool. So we don't need a special case
check in the completion handler.