Re: [PATCH v1 0/5] dm: dm-user: New target that proxies BIOs to userspace

[Mike Snitzer]

On Tue, Dec 22 2020 at  8:32am -0500,
Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:

> On Mon, Dec 14, 2020 at 07:00:57PM -0800, Palmer Dabbelt wrote:
> > I haven't gotten a whole lot of feedback, so I'm inclined to at least have some
> > reasonable performance numbers before bothering with a v2.
> 
> FYI, my other main worry beside duplicating nbd is that device mapper
> really is a stacked interface that sits on top of other block device.
> Turning this into something else that just pipes data to userspace
> seems very strange.

I agree.  Only way I'd be interested is if it somehow tackled enabling
much more efficient IO.  Earlier discussion in this thread mentioned
that zero-copy and low overhead wasn't a priority (because it is hard,
etc).  But the hard work has already been done with io_uring.  If
dm-user had a prereq of leaning heavily on io_uring and also enabled IO
polling for bio-based then there may be a win to supporting it.

But unless lower latency (or some other more significant win) is made
possible I just don't care to prop up an unnatural DM bolt-on.

Mike