On Fri, Feb 11 2022 at 10:01P -0500,
Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> Exactly the same sector number and length must be passed to both calls of
> dm_stats_account_io, otherwise its per-zone in_flight counters go out of
> sync. This patch fixes it.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> ---
> drivers/md/dm.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> Index: linux-dm/drivers/md/dm.c
> ===================================================================
> --- linux-dm.orig/drivers/md/dm.c 2022-02-11 15:32:56.000000000 +0100
> +++ linux-dm/drivers/md/dm.c 2022-02-11 15:40:11.000000000 +0100
> @@ -487,16 +487,20 @@ EXPORT_SYMBOL_GPL(dm_start_time_ns_from_
>
> static void start_io_acct(struct dm_io *io, struct bio *bio)
> {
> + struct bio *orig_bio;
> +
> /* Ensure IO accounting is only ever started once */
> if (xchg(&io->was_accounted, 1) == 1)
> return;
>
> + orig_bio = io->orig_bio;
> +
> bio_start_io_acct_remapped(bio, io->start_time,
> - io->orig_bio->bi_bdev);
> + orig_bio->bi_bdev);
>
> if (unlikely(dm_stats_used(&io->md->stats)))
> - dm_stats_account_io(&io->md->stats, bio_data_dir(bio),
> - bio->bi_iter.bi_sector, bio_sectors(bio),
> + dm_stats_account_io(&io->md->stats, bio_data_dir(orig_bio),
> + orig_bio->bi_iter.bi_sector, bio_sectors(orig_bio),
> false, 0, &io->stats_aux);
> }
>
>
You cannot account using the orig_bio because it doesn't reflect
splits that occurred. orig_bio will be updated to reflect the split
after __map_bio returns all the way back to dm_split_and_process_bio.
So there is no imbalance between start_io_acct and end_io_acct's calls
to dm_stats_account_io.
Also, in_flight counters don't (or shouldn't) care about the payload.
So again, I'm not following the reasoning on this patch.
Mike
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