[PATCH v4 0/3] block/dm: fix bio-based DM IO accounting

From: Mike Snitzer <snitzer@redhat.com>
To: axboe@kernel.dk
Cc: hch@lst.de, dm-devel@redhat.com, linux-block@vger.kernel.org
Subject: [PATCH v4 0/3] block/dm: fix bio-based DM IO accounting
Date: Fri, 28 Jan 2022 10:58:38 -0500	[thread overview]
Message-ID: <20220128155841.39644-1-snitzer@redhat.com> (raw)

[this v4 is final iteration, should be "ready"...]

Hi Jens,

Just over 3 years ago, with commit a1e1cb72d9649 ("dm: fix redundant
IO accounting for bios that need splitting") I focused too narrowly on
fixing the reported potential for redundant accounting for IO totals.
Which, at least mentally for me, papered over how inaccurate all other
bio-based DM's IO accounting is for bios that get split.

This set fixes things up properly by allowing DM to start IO
accounting _after_ IO is submitted and a split may have occurred. The
proper start_time is still established (prior to submission), it is
passed in to a new bio_start_io_acct_time().  This eliminates the need
for any DM hack to rewind block core's accounting that was started
before any potential bio split.

All said: If you'd provide your Acked-by(s) I'm happy to send this set
to Linus for v5.17-rc (and shepherd the changes into stable@ kernels).

Or you're welcome to pickup this set to send along (I'd obviously
still do any stable@ backports). NOTE: the 3rd patch references the
linux-dm.git commit id for the 1st patch.. so that'll require tweaking
no matter who sends the changes to Linus.

Please advise, thanks.
Mike

v4: added Christoph's Reviewed-bys. Removed READ_ONCE from patch 3
v3: fix patch 3 to call bio_start_io_acct_time
v2: made block changes suggested by Christoph

Mike Snitzer (3):
  block: add bio_start_io_acct_time() to control start_time
  dm: revert partial fix for redundant bio-based IO accounting
  dm: properly fix redundant bio-based IO accounting

 block/blk-core.c       | 25 +++++++++++++++++++------
 drivers/md/dm.c        | 20 +++-----------------
 include/linux/blkdev.h |  1 +
 3 files changed, 23 insertions(+), 23 deletions(-)

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2.15.0