On Thu, 29 Nov 2018, Mike Snitzer wrote:
> On Tue, Nov 27 2018 at 7:42pm -0500,
> Mikulas Patocka <mpato...@redhat.com> wrote:
>
> > Now when part_round_stats is gone, we can switch to per-cpu in-flight
> > counters.
> >
> > We use the local-atomic type local_t, so that if part_inc_in_flight or
> > part_dec_in_flight is reentrantly called from an interrupt, the value will
> > be correct.
> >
> > The other counters could be corrupted due to reentrant interrupt, but the
> > corruption only results in slight counter skew - the in_flight counter
> > must be exact, so it needs local_t.
> >
> > Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
> >
> > ---
> > block/bio.c | 4 ++--
> > block/blk-core.c | 4 ++--
> > block/blk-merge.c | 2 +-
> > block/genhd.c | 47
> > +++++++++++++++++++++++++++++++++++------------
> > drivers/md/dm.c | 4 +---
> > include/linux/genhd.h | 7 ++++---
> > 6 files changed, 45 insertions(+), 23 deletions(-)
> >
> ...
> > Index: linux-block/drivers/md/dm.c
> > ===================================================================
> > --- linux-block.orig/drivers/md/dm.c 2018-11-28 00:09:59.000000000
> > +0100
> > +++ linux-block/drivers/md/dm.c 2018-11-28 00:09:59.000000000 +0100
> > @@ -663,8 +663,7 @@ static void start_io_acct(struct dm_io *
> > generic_start_io_acct(md->queue, bio_op(bio), bio_sectors(bio),
> > &dm_disk(md)->part0);
> >
> > - atomic_set(&dm_disk(md)->part0.in_flight[rw],
> > - atomic_inc_return(&md->pending[rw]));
> > + atomic_inc(&md->pending[rw]);
> >
> > if (unlikely(dm_stats_used(&md->stats)))
> > dm_stats_account_io(&md->stats, bio_data_dir(bio),
> > @@ -693,7 +692,6 @@ static void end_io_acct(struct dm_io *io
> > * a flush.
> > */
> > pending = atomic_dec_return(&md->pending[rw]);
> > - atomic_set(&dm_disk(md)->part0.in_flight[rw], pending);
> > pending += atomic_read(&md->pending[rw^0x1]);
> >
> > /* nudge anyone waiting on suspend queue */
> >
>
>
> These dm.c hunks conflict with changes from you that I already staged in
> dm-4.21, see:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.21&id=b5616f7a11592cc74860f4ec3e3c4fba6688eefa
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.21&id=78f95b53c203c969bbe6b86e405f7a891a43b6be
>
> I'd really like to get away from DM maintaining its own ->pending
> counters.
>
> Mike
I know.
It depends on whether Jens takes these patches or not. If he doesn't take
them, dm will use percpu counters on its own and it will return zero in
the "/sys/block/dm-*/inflight" file.
Mikulas
