[v2,0/3] block/dm: fix bio-based DM IO accounting

Message

Mike Snitzer Jan. 27, 2022, 10:56 p.m. UTC

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 is 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 excessive accounting in the
face of a split bio recursing back to block core.

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

v1 -> 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(-)