Re: [PATCH v3 2/3] dm: Add support for block provisioning

Sarthak Kukreti
2023-04-18T22:14:09Z

On Fri, Apr 14, 2023 at 2:58 PM Mike Snitzer <snitzer@kernel.org> wrote:
>
> On Thu, Apr 13 2023 at 8:02P -0400,
> Sarthak Kukreti <sarthakkukreti@chromium.org> wrote:
>
> > Add support to dm devices for REQ_OP_PROVISION. The default mode
> > is to passthrough the request to the underlying device, if it
> > supports it. dm-thinpool uses the provision request to provision
> > blocks for a dm-thin device. dm-thinpool currently does not
> > pass through REQ_OP_PROVISION to underlying devices.
> >
> > For shared blocks, provision requests will break sharing and copy the
> > contents of the entire block.
> >
> > Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> > ---
> > drivers/md/dm-crypt.c | 4 +-
> > drivers/md/dm-linear.c | 1 +
> > drivers/md/dm-snap.c | 7 +++
>
> Have you tested REQ_OP_PROVISION with these targets? Just want to
> make sure you have an explicit need (and vested interest) for them
> passing through REQ_OP_PROVISION.
>

Yes. I have a vested interest in dm-linear and dm-crypt; I kept
dm-snap support mostly for consistency with thin snapshots.

> > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> > index 2055a758541d..5985343384a7 100644
> > --- a/drivers/md/dm-table.c
> > +++ b/drivers/md/dm-table.c
> > @@ -1850,6 +1850,26 @@ static bool dm_table_supports_write_zeroes(struct dm_table *t)
> > return true;
> > }
> >
> > +static int device_provision_capable(struct dm_target *ti, struct dm_dev *dev,
> > + sector_t start, sector_t len, void *data)
> > +{
> > + return !bdev_max_provision_sectors(dev->bdev);
> > +}
> > +
> > +static bool dm_table_supports_provision(struct dm_table *t)
> > +{
> > + for (unsigned int i = 0; i < t->num_targets; i++) {
> > + struct dm_target *ti = dm_table_get_target(t, i);
> > +
> > + if (ti->provision_supported ||
> > + (ti->type->iterate_devices &&
> > + ti->type->iterate_devices(ti, device_provision_capable, NULL)))
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > +
> > static int device_not_nowait_capable(struct dm_target *ti, struct dm_dev *dev,
> > sector_t start, sector_t len, void *data)
> > {
> > @@ -1983,6 +2003,11 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
> > if (!dm_table_supports_write_zeroes(t))
> > q->limits.max_write_zeroes_sectors = 0;
> >
> > + if (dm_table_supports_provision(t))
> > + blk_queue_max_provision_sectors(q, UINT_MAX >> 9);
>
> This doesn't seem correct in that it'll override whatever
> max_provision_sectors was set by a target (like thinp).
>
> I think you only need the if (!dm_table_supports_provision)) case:
>
Done

> > + else
> > + q->limits.max_provision_sectors = 0;
> > +
> > dm_table_verify_integrity(t);
> >
> > /*
> > diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> > index 13d4677baafd..b08b7ae617be 100644
> > --- a/drivers/md/dm-thin.c
> > +++ b/drivers/md/dm-thin.c
>
> I think it'll make the most sense to split out the dm-thin.c changes
> in a separate patch.
>
Separated the dm-thin changes into a separate patch that follows this one in v4.

> > @@ -909,7 +909,8 @@ static void __inc_remap_and_issue_cell(void *context,
> > struct bio *bio;
> >
> > while ((bio = bio_list_pop(&cell->bios))) {
> > - 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)
> > bio_list_add(&info->defer_bios, bio);
> > else {
> > inc_all_io_entry(info->tc->pool, bio);
> > @@ -1013,6 +1014,15 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
> > goto out;
> > }
> >
> > + /*
> > + * For provision requests, once the prepared block has been inserted
> > + * into the mapping btree, return.
> > + */
> > + if (bio && bio_op(bio) == REQ_OP_PROVISION) {
> > + bio_endio(bio);
> > + return;
> > + }
> > +
> > /*
> > * Release any bios held while the block was being provisioned.
> > * If we are processing a write bio that completely covers the block,
> > @@ -1241,7 +1251,7 @@ static int io_overlaps_block(struct pool *pool, struct bio *bio)
> >
> > static int io_overwrites_block(struct pool *pool, struct bio *bio)
> > {
> > - return (bio_data_dir(bio) == WRITE) &&
> > + return (bio_data_dir(bio) == WRITE) && bio_op(bio) != REQ_OP_PROVISION &&
> > io_overlaps_block(pool, bio);
> > }
> >
> > @@ -1334,10 +1344,11 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
> > /*
> > * IO to pool_dev remaps to the pool target's data_dev.
> > *
> > - * If the whole block of data is being overwritten, we can issue the
> > - * bio immediately. Otherwise we use kcopyd to clone the data first.
> > + * If the whole block of data is being overwritten and if this is not a
> > + * provision request, we can issue the bio immediately.
> > + * Otherwise we use kcopyd to clone the data first.
> > */
> > - if (io_overwrites_block(pool, bio))
> > + if (io_overwrites_block(pool, bio) && bio_op(bio) != REQ_OP_PROVISION)
> > remap_and_issue_overwrite(tc, bio, data_dest, m);
> > else {
> > struct dm_io_region from, to;
> > @@ -1356,7 +1367,8 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
> > /*
> > * Do we need to zero a tail region?
> > */
> > - if (len < pool->sectors_per_block && pool->pf.zero_new_blocks) {
> > + if (len < pool->sectors_per_block && pool->pf.zero_new_blocks &&
> > + bio_op(bio) != REQ_OP_PROVISION) {
> > atomic_inc(&m->prepare_actions);
> > ll_zero(tc, m,
> > data_dest * pool->sectors_per_block + len,
> > @@ -1390,6 +1402,10 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
> > m->data_block = data_block;
> > m->cell = cell;
> >
> > + /* Provision requests are chained on the original bio. */
> > + if (bio && bio_op(bio) == REQ_OP_PROVISION)
> > + m->bio = bio;
> > +
> > /*
> > * If the whole block of data is being overwritten or we are not
> > * zeroing pre-existing data, we can issue the bio immediately.
> > @@ -1865,7 +1881,8 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
> >
> > if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size) {
> > break_sharing(tc, bio, block, &key, lookup_result, data_cell);
> > - cell_defer_no_holder(tc, virt_cell);
> > + if (bio_op(bio) != REQ_OP_PROVISION)
> > + cell_defer_no_holder(tc, virt_cell);
> > } else {
> > struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
> >
>
> Not confident in the above changes given the request that we only
> handle REQ_OP_PROVISION one thinp block at a time. So I'll gloss over
> them for now.
>
Yeah, the majority of this got removed in v4. I added a check in
io_overwrites_block() to return false for all provision requests.

> > @@ -1982,6 +1999,73 @@ 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);
> > + switch (r) {
> > + case 0:
> > + if (lookup_result.shared)
> > + process_shared_bio(tc, bio, begin,
> > + &lookup_result, cell);
> > + 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;
> > + }
>
> Like Joe mentioned, this pattern was fine for discards because they
> are advisory/optional. But we need to make sure we don't truncate
> REQ_OP_PROVISION -- so we need to round up if we partially bleed into
> the blocks to the left or right.
>
> BUT ranged REQ_OP_PROVISION support is for later, this can be dealt
> with more simply in that each REQ_OP_PROVISION will be handled a block
> at a time initially. SO you'll want to honor _all_ REQ_OP_PROVISION,
> never returning early.
>
Thanks. The next patch in the series has the simplified version. It
had a lot in common with process_bio() so there was a possibility for
merging the two code paths, but I opted to keep it like this to make
ranged handling and passdown support easier to implement.

> > +
> > + 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;
> > @@ -2202,6 +2286,8 @@ 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);
>
> This should be pool->process_provision() (or ->process_provision_bio
> if you like). Point is, you need to be switching these methods
> if/when the pool_mode transitions in set_pool_mode().
>
Done

> > else
> > pool->process_bio(tc, bio);
> >
> > @@ -2723,7 +2809,8 @@ 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;
> > }
> > @@ -3370,6 +3457,8 @@ static int pool_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> > pt->adjusted_pf = pt->requested_pf = pf;
> > ti->num_flush_bios = 1;
> > ti->limit_swap_bios = true;
> > + ti->num_provision_bios = 1;
> > + ti->provision_supported = true;
> >
> > /*
> > * Only need to enable discards if the pool should pass
> > @@ -4068,6 +4157,7 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
> > blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
> > }
> >
> > +
>
> Please fix this extra whitespace damage.
>
Done

> > /*
> > * pt->adjusted_pf is a staging area for the actual features to use.
> > * They get transferred to the live pool in bind_control_target()
> > @@ -4261,6 +4351,9 @@ static int thin_ctr(struct dm_target *ti, unsigned int 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);
> > @@ -4475,6 +4568,7 @@ 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 */
>
> Building on my previous reply, with suggested update to
> dm.c:__process_abnormal_io(), once you rebase on dm-6.4's dm-thin.c
> you'll want to instead:
>
> limits->max_provision_sectors = pool->sectors_per_block << SECTOR_SHIFT;
>
> And you'll want to drop any of the above code that deals with handling
> bio-prison range locking and processing of REQ_OP_PROVISION for
> multiple thinp blocks at once.
>
> Simple REQ_OP_PROVISION processing one thinp block at a time first and
> then we can worry about handling REQ_OP_PROVISION that span blocks
> later.
>
Thanks, done in v4.

> > static struct target_type thin_target = {
> > diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> > index dfde0088147a..d8f1803062b7 100644
> > --- a/drivers/md/dm.c
> > +++ b/drivers/md/dm.c
> > @@ -1593,6 +1593,7 @@ 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;
> > @@ -1617,6 +1618,9 @@ 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;
> > }
>
> Please be sure to include my suggested __process_abnormal_io change
> from my previous reply.
>
Done.

> > diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> > index 7975483816e4..e9f687521ae6 100644
> > --- a/include/linux/device-mapper.h
> > +++ b/include/linux/device-mapper.h
> > @@ -334,6 +334,12 @@ struct dm_target {
> > */
> > unsigned int 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 int num_provision_bios;
> > +
> > /*
> > * The minimum number of extra bytes allocated in each io for the
> > * target to use.
> > @@ -358,6 +364,11 @@ 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.
> > */
>
> You'll need to add max_provision_granularity bool too (as implied by
> the dm.c:__process_abnormal_io() change suggested in my first reply to
> this patch).
>
> I'm happy to wait for you to consume the v3 feedback we've provided so
> you can create a v4. I'm thinking I can base dm-thin.c's WRITE_ZEROES
> support ontop of your REQ_OP_PROVISION v4 changes -- they should be
> complementary.
>
Done. Thanks for the review and guidance!

Best
Sarthak

> Thanks,
> Mike