Re: [dm-devel] [PATCH, RFC] block: don't allocate a payload for discard request

[Mike Snitzer <snitzer redhat com>]

On Fri, Jun 18 2010 at 10:59am -0400,
Christoph Hellwig <hch lst de> wrote:

> 
> Allocating a fixed payload for discard requests always was a horrible hack,
> and it's not coming to byte us when adding support for discard in DM/MD.
> 
> So change the code to leave the allocation of a payload to the lowlevel
> driver.  Unfortunately that means we'll need another hack, which allows
> us to update the various block layer length fields indicating that we
> have a payload.  Instead of hiding this in sd.c, which we already partially
> do for UNMAP support add a documented helper in the core block layer for it.
> 
> Signed-off-by: Christoph Hellwig <hch lst de>

Acked-by: Mike Snitzer <snitzer redhat com>

I've built on your patch to successfully implement discard support for
DM (this includes splitting discards that span targets; only the linear
and striped DM targets are supported so far).

The patchset is still a work in progress but is available here (against
2.6.34 at the moment):
http://people.redhat.com/msnitzer/patches/dm-discard/latest/