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

Mike Snitzer
2023-04-14T21:59:36Z

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.

> 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:

> + 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.

> @@ -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.

> @@ -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.

> +
> + 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().

> 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.

> /*
> * 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.

> 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.

> 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.

Thanks,
Mike