[dm-devel] [PATCH v3] block, dm: don't copy bios for request clones

[Mike Snitzer]

On Mon, Apr 27 2015 at  8:59pm -0400,
Mike Snitzer <snitzer at redhat.com> wrote:

> From: Christoph Hellwig <hch at lst.de>
> 
> Currently dm-multipath has to clone the bios for every request sent
> to the lower devices, which wastes cpu cycles and ties down memory.
> 
> This patch instead adds a new REQ_CLONE flag that instructs req_bio_endio
> to not complete bios attached to a request, which we set on clone
> requests similar to bios in a flush sequence.  With this change I/O
> errors on a path failure only get propagated to dm-multipath, which
> can then either resubmit the I/O or complete the bios on the original
> request.
> 
> I've done some basic testing of this on a Linux target with ALUA support,
> and it survives path failures during I/O nicely.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
> ---
>  block/blk-core.c          |  94 +++----------------------
>  drivers/md/dm-table.c     |  25 ++++---
>  drivers/md/dm.c           | 171 +++++++++++-----------------------------------
>  drivers/md/dm.h           |   5 +-
>  include/linux/blk_types.h |   2 +
>  include/linux/blkdev.h    |   6 +-
>  6 files changed, 73 insertions(+), 230 deletions(-)
> 
> v3: really just some line-wrapping, whitespace, and misc small nits

Hey Jens,

Given the blk-core changes, would you like to pick this up for 4.2 and
I'll just base DM ontop of linux-block.git again for the 4.2 cycle?

The patch is available here: https://patchwork.kernel.org/patch/6285081/

Mike

p.s. I do have a followup DM patch that cleans things up further but I
can just stage it via linux-dm.git:
https://patchwork.kernel.org/patch/6285091/