Re: [PATCH v2 2/7] dm: Add support for block provisioning

[Sarthak Kukreti]

On Thu, Jan 5, 2023 at 6:42 AM Brian Foster <bfoster@xxxxxxxxxx> wrote:
>
> On Thu, Dec 29, 2022 at 12:12:47AM -0800, Sarthak Kukreti wrote:
> > Add support to dm devices for REQ_OP_PROVISION. The default mode
> > is to pass through the request and dm-thin will utilize it to provision
> > blocks.
> >
> > Signed-off-by: Sarthak Kukreti <sarthakkukreti@xxxxxxxxxxxx>
> > ---
> >  drivers/md/dm-crypt.c         |  4 +-
> >  drivers/md/dm-linear.c        |  1 +
> >  drivers/md/dm-snap.c          |  7 +++
> >  drivers/md/dm-table.c         | 25 ++++++++++
> >  drivers/md/dm-thin.c          | 90 ++++++++++++++++++++++++++++++++++-
> >  drivers/md/dm.c               |  4 ++
> >  include/linux/device-mapper.h | 11 +++++
> >  7 files changed, 139 insertions(+), 3 deletions(-)
> >
> ...
> > diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> > index 64cfcf46881d..ab3f1abfabaf 100644
> > --- a/drivers/md/dm-thin.c
> > +++ b/drivers/md/dm-thin.c
> ...
> > @@ -1980,6 +1992,70 @@ static void process_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
> >       }
> >  }
> >
> > +static void process_provision_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
> > +{
> > +     int r;
> > +     struct pool *pool = tc->pool;
> > +     struct bio *bio = cell->holder;
> > +     dm_block_t begin, end;
> > +     struct dm_thin_lookup_result lookup_result;
> > +
> > +     if (tc->requeue_mode) {
> > +             cell_requeue(pool, cell);
> > +             return;
> > +     }
> > +
> > +     get_bio_block_range(tc, bio, &begin, &end);
> > +
> > +     while (begin != end) {
> > +             r = ensure_next_mapping(pool);
> > +             if (r)
> > +                     /* we did our best */
> > +                     return;
> > +
> > +             r = dm_thin_find_block(tc->td, begin, 1, &lookup_result);
>
> Hi Sarthak,
>
> I think we discussed this before.. but remind me if/how we wanted to
> handle the case if the thin blocks are shared..? Would a provision op
> carry enough information to distinguish an FALLOC_FL_UNSHARE_RANGE
> request from upper layers to conditionally provision in that case?
>
I think that should depend on how the filesystem implements unsharing:
assuming that we use provision on first allocation, unsharing on xfs
should result in xfs calling REQ_OP_PROVISION on the newly allocated
blocks first. But for ext4, we'd fail UNSHARE_RANGE unless provision
(instead of noprovision, provision_on_alloc), in which case, we'd send
REQ_OP_PROVISION.

Best
Sarthak


Sarthak

> Brian
>
> > +             switch (r) {
> > +             case 0:
> > +                     begin++;
> > +                     break;
> > +             case -ENODATA:
> > +                     bio_inc_remaining(bio);
> > +                     provision_block(tc, bio, begin, cell);
> > +                     begin++;
> > +                     break;
> > +             default:
> > +                     DMERR_LIMIT(
> > +                             "%s: dm_thin_find_block() failed: error = %d",
> > +                             __func__, r);
> > +                     cell_defer_no_holder(tc, cell);
> > +                     bio_io_error(bio);
> > +                     begin++;
> > +                     break;
> > +             }
> > +     }
> > +     bio_endio(bio);
> > +     cell_defer_no_holder(tc, cell);
> > +}
> > +
> > +static void process_provision_bio(struct thin_c *tc, struct bio *bio)
> > +{
> > +     dm_block_t begin, end;
> > +     struct dm_cell_key virt_key;
> > +     struct dm_bio_prison_cell *virt_cell;
> > +
> > +     get_bio_block_range(tc, bio, &begin, &end);
> > +     if (begin == end) {
> > +             bio_endio(bio);
> > +             return;
> > +     }
> > +
> > +     build_key(tc->td, VIRTUAL, begin, end, &virt_key);
> > +     if (bio_detain(tc->pool, &virt_key, bio, &virt_cell))
> > +             return;
> > +
> > +     process_provision_cell(tc, virt_cell);
> > +}
> > +
> >  static void process_bio(struct thin_c *tc, struct bio *bio)
> >  {
> >       struct pool *pool = tc->pool;
> > @@ -2200,6 +2276,8 @@ static void process_thin_deferred_bios(struct thin_c *tc)
> >
> >               if (bio_op(bio) == REQ_OP_DISCARD)
> >                       pool->process_discard(tc, bio);
> > +             else if (bio_op(bio) == REQ_OP_PROVISION)
> > +                     process_provision_bio(tc, bio);
> >               else
> >                       pool->process_bio(tc, bio);
> >
> > @@ -2716,7 +2794,8 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
> >               return DM_MAPIO_SUBMITTED;
> >       }
> >
> > -     if (op_is_flush(bio->bi_opf) || bio_op(bio) == REQ_OP_DISCARD) {
> > +     if (op_is_flush(bio->bi_opf) || bio_op(bio) == REQ_OP_DISCARD ||
> > +         bio_op(bio) == REQ_OP_PROVISION) {
> >               thin_defer_bio_with_throttle(tc, bio);
> >               return DM_MAPIO_SUBMITTED;
> >       }
> > @@ -3355,6 +3434,8 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
> >       pt->low_water_blocks = low_water_blocks;
> >       pt->adjusted_pf = pt->requested_pf = pf;
> >       ti->num_flush_bios = 1;
> > +     ti->num_provision_bios = 1;
> > +     ti->provision_supported = true;
> >
> >       /*
> >        * Only need to enable discards if the pool should pass
> > @@ -4053,6 +4134,7 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
> >               blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
> >       }
> >
> > +
> >       /*
> >        * pt->adjusted_pf is a staging area for the actual features to use.
> >        * They get transferred to the live pool in bind_control_target()
> > @@ -4243,6 +4325,9 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
> >               ti->num_discard_bios = 1;
> >       }
> >
> > +     ti->num_provision_bios = 1;
> > +     ti->provision_supported = true;
> > +
> >       mutex_unlock(&dm_thin_pool_table.mutex);
> >
> >       spin_lock_irq(&tc->pool->lock);
> > @@ -4457,6 +4542,7 @@ static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
> >
> >       limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
> >       limits->max_discard_sectors = 2048 * 1024 * 16; /* 16G */
> > +     limits->max_provision_sectors = 2048 * 1024 * 16; /* 16G */
> >  }
> >
> >  static struct target_type thin_target = {
> > diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> > index e1ea3a7bd9d9..4d19bae9da4a 100644
> > --- a/drivers/md/dm.c
> > +++ b/drivers/md/dm.c
> > @@ -1587,6 +1587,7 @@ static bool is_abnormal_io(struct bio *bio)
> >               case REQ_OP_DISCARD:
> >               case REQ_OP_SECURE_ERASE:
> >               case REQ_OP_WRITE_ZEROES:
> > +             case REQ_OP_PROVISION:
> >                       return true;
> >               default:
> >                       break;
> > @@ -1611,6 +1612,9 @@ static blk_status_t __process_abnormal_io(struct clone_info *ci,
> >       case REQ_OP_WRITE_ZEROES:
> >               num_bios = ti->num_write_zeroes_bios;
> >               break;
> > +     case REQ_OP_PROVISION:
> > +             num_bios = ti->num_provision_bios;
> > +             break;
> >       default:
> >               break;
> >       }
> > diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> > index 04c6acf7faaa..b4d97d5d75b8 100644
> > --- a/include/linux/device-mapper.h
> > +++ b/include/linux/device-mapper.h
> > @@ -333,6 +333,12 @@ struct dm_target {
> >        */
> >       unsigned num_write_zeroes_bios;
> >
> > +     /*
> > +      * The number of PROVISION bios that will be submitted to the target.
> > +      * The bio number can be accessed with dm_bio_get_target_bio_nr.
> > +      */
> > +     unsigned num_provision_bios;
> > +
> >       /*
> >        * The minimum number of extra bytes allocated in each io for the
> >        * target to use.
> > @@ -357,6 +363,11 @@ struct dm_target {
> >        */
> >       bool discards_supported:1;
> >
> > +     /* Set if this target needs to receive provision requests regardless of
> > +      * whether or not its underlying devices have support.
> > +      */
> > +     bool provision_supported:1;
> > +
> >       /*
> >        * Set if we need to limit the number of in-flight bios when swapping.
> >        */
> > --
> > 2.37.3
> >
>