[dm-devel] [RFC PATCH V2 3/3] dm: support bio polling
JeffleXu
jefflexu at linux.alibaba.com
Fri Jun 18 08:19:10 UTC 2021
On 6/17/21 6:35 PM, Ming Lei wrote:
> Support bio(REQ_POLLED) polling in the following approach:
>
> 1) only support io polling on normal READ/WRITE, and other abnormal IOs
> still fallback on IRQ mode, so the target io is exactly inside the dm
> io.
>
> 2) hold one refcnt on io->io_count after submitting this dm bio with
> REQ_POLLED
>
> 3) support dm native bio splitting, any dm io instance associated with
> current bio will be added into one list which head is bio->bi_end_io
> which will be recovered before ending this bio
>
> 4) implement .poll_bio() callback, call bio_poll() on the single target
> bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call
> dec_pending() after the target io is done in .poll_bio()
>
> 4) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL,
> which is based on Jeffle's previous patch.
>
> Signed-off-by: Ming Lei <ming.lei at redhat.com>
> ---
> drivers/md/dm-table.c | 24 +++++++++
> drivers/md/dm.c | 111 ++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 132 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index ee47a332b462..b14b379442d2 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1491,6 +1491,12 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
> return &t->targets[(KEYS_PER_NODE * n) + k];
> }
>
> +static int device_not_poll_capable(struct dm_target *ti, struct dm_dev *dev,
> + sector_t start, sector_t len, void *data)
> +{
> + return !blk_queue_poll(bdev_get_queue(dev->bdev));
> +}
> +
> /*
> * type->iterate_devices() should be called when the sanity check needs to
> * iterate and check all underlying data devices. iterate_devices() will
> @@ -1541,6 +1547,11 @@ static int count_device(struct dm_target *ti, struct dm_dev *dev,
> return 0;
> }
>
> +static int dm_table_supports_poll(struct dm_table *t)
> +{
> + return !dm_table_any_dev_attr(t, device_not_poll_capable, NULL);
> +}
> +
> /*
> * Check whether a table has no data devices attached using each
> * target's iterate_devices method.
> @@ -2078,6 +2089,19 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>
> dm_update_keyslot_manager(q, t);
> blk_queue_update_readahead(q);
> +
> + /*
> + * Check for request-based device is remained to
> + * dm_mq_init_request_queue()->blk_mq_init_allocated_queue().
> + * For bio-based device, only set QUEUE_FLAG_POLL when all underlying
> + * devices supporting polling.
> + */
> + if (__table_type_bio_based(t->type)) {
> + if (dm_table_supports_poll(t))
> + blk_queue_flag_set(QUEUE_FLAG_POLL, q);
> + else
> + blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
> + }
> }
>
> unsigned int dm_table_get_num_targets(struct dm_table *t)
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 363f12a285ce..9745c3deacc3 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -39,6 +39,8 @@
> #define DM_COOKIE_ENV_VAR_NAME "DM_COOKIE"
> #define DM_COOKIE_LENGTH 24
>
> +#define REQ_SAVED_END_IO REQ_DRV
> +
> static const char *_name = DM_NAME;
>
> static unsigned int major = 0;
> @@ -97,8 +99,11 @@ struct dm_io {
> unsigned magic;
> struct mapped_device *md;
> blk_status_t status;
> + bool submit_as_polled;
> atomic_t io_count;
> struct bio *orig_bio;
> + void *saved_bio_end_io;
> + struct hlist_node node;
> unsigned long start_time;
> spinlock_t endio_lock;
> struct dm_stats_aux stats_aux;
> @@ -687,6 +692,8 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci, struct dm_target *t
> tio->ti = ti;
> tio->target_bio_nr = target_bio_nr;
>
> + WARN_ON_ONCE(ci->io->submit_as_polled && !tio->inside_dm_io);
> +
> return tio;
> }
>
> @@ -938,8 +945,12 @@ static void dec_pending(struct dm_io *io, blk_status_t error)
> end_io_acct(io);
> free_io(md, io);
>
> - if (io_error == BLK_STS_DM_REQUEUE)
> + if (io_error == BLK_STS_DM_REQUEUE) {
> + /* not poll any more in case of requeue */
> + if (bio->bi_opf & REQ_POLLED)
> + bio->bi_opf &= ~REQ_POLLED;
> return;
> + }
Actually I'm not sure why REQ_POLLED should be cleared here.
Besides, there's one corner case where bio is submitted when dm device
is suspended.
```
static blk_qc_t dm_submit_bio(struct bio *bio)
/* If suspended, queue this IO for later */
if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
if (bio->bi_opf & REQ_NOWAIT)
bio_wouldblock_error(bio);
else if (bio->bi_opf & REQ_RAHEAD)
bio_io_error(bio);
else
queue_io(md, bio);
goto out;
}
```
When the dm device is suspended with DMF_BLOCK_IO_FOR_SUSPEND, the
submitted bio is inserted into @md->deferred list by calling queue_io().
Then the following bio_poll() calling will trigger the
'WARN_ON_ONCE(!saved_bi_end_io)' in dm_poll_bio(), if the previously
submitted bio is still buffered in @md->deferred list.
```
submit_bio()
dm_submit_bio
queue_io
bio_poll
dm_poll_bio
```
>
> if ((bio->bi_opf & REQ_PREFLUSH) && bio->bi_iter.bi_size) {
> /*
> @@ -1590,6 +1601,12 @@ static int __split_and_process_non_flush(struct clone_info *ci)
> if (__process_abnormal_io(ci, ti, &r))
> return r;
>
> + /*
> + * Only support bio polling for normal IO, and the target io is
> + * exactly inside the dm io instance
> + */
> + ci->io->submit_as_polled = !!(ci->bio->bi_opf & REQ_POLLED);
> +
> len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count);
>
> r = __clone_and_map_data_bio(ci, ti, ci->sector, &len);
> @@ -1608,6 +1625,22 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md,
> ci->map = map;
> ci->io = alloc_io(md, bio);
> ci->sector = bio->bi_iter.bi_sector;
> +
> + if (bio->bi_opf & REQ_POLLED) {
> + INIT_HLIST_NODE(&ci->io->node);
> +
> + /*
> + * Save .bi_end_io into dm_io, so that we can reuse .bi_end_io
> + * for storing dm_io list
> + */
> + if (bio->bi_opf & REQ_SAVED_END_IO) {
> + ci->io->saved_bio_end_io = NULL;
> + } else {
> + ci->io->saved_bio_end_io = bio->bi_end_io;
> + INIT_HLIST_HEAD((struct hlist_head *)&bio->bi_end_io);
> + bio->bi_opf |= REQ_SAVED_END_IO;
> + }
> + }
> }
>
> #define __dm_part_stat_sub(part, field, subnd) \
> @@ -1666,8 +1699,19 @@ static void __split_and_process_bio(struct mapped_device *md,
> }
> }
>
> - /* drop the extra reference count */
> - dec_pending(ci.io, errno_to_blk_status(error));
> + /*
> + * Drop the extra reference count for non-POLLED bio, and hold one
> + * reference for POLLED bio, which will be released in dm_poll_bio
> + *
> + * Add every dm_io instance into the hlist_head which is stored in
> + * bio->bi_end_io, so that dm_poll_bio can poll them all.
> + */
> + if (!ci.io->submit_as_polled)
> + dec_pending(ci.io, errno_to_blk_status(error));
> + else
> + hlist_add_head(&ci.io->node,
> + (struct hlist_head *)&bio->bi_end_io);
> +
> }
>
> static void dm_submit_bio(struct bio *bio)
> @@ -1707,6 +1751,66 @@ static void dm_submit_bio(struct bio *bio)
> dm_put_live_table(md, srcu_idx);
> }
>
> +static int dm_poll_dm_io(struct dm_io *io, unsigned int flags)
> +{
> + if (!io || !io->submit_as_polled)
> + return 0;
Wondering if '!io->submit_as_polled' is necessary here. dm_io will be
added into the hash list only when 'io->submit_as_polled' is true in
__split_and_process_bio.
> +
> + WARN_ON_ONCE(!io->tio.inside_dm_io);
> + bio_poll(&io->tio.clone, flags);
> +
> + /* bio_poll holds the last reference */
> + if (atomic_read(&io->io_count) == 1)
> + return 1;
> + return 0;
> +}
> +
> +static int dm_poll_bio(struct bio *bio, unsigned int flags)
> +{
> + struct dm_io *io;
> + void *saved_bi_end_io = NULL;
> + struct hlist_head tmp = HLIST_HEAD_INIT;
> + struct hlist_head *head = (struct hlist_head *)&bio->bi_end_io;
> + struct hlist_node *next;
> +
> + /*
> + * This bio can be submitted from FS as POLLED so that FS may keep
> + * polling even though the flag is cleared by bio splitting or
> + * requeue, so return immediately.
> + */
> + if (!(bio->bi_opf & REQ_POLLED))
> + return 0;
> +
> + hlist_move_list(head, &tmp);
> +
> + hlist_for_each_entry(io, &tmp, node) {
> + if (io->saved_bio_end_io && !saved_bi_end_io) {
Seems that checking if saved_bi_end_io NULL here is not necessary, since
you will exit thte loop once saved_bi_end_io is assigned.
> + saved_bi_end_io = io->saved_bio_end_io;
> + break;
> + }
> + }
> +
> + /* restore .bi_end_io before completing dm io */
> + WARN_ON_ONCE(!saved_bi_end_io);
Abnormal bio flagged with REQ_POLLED (is this possible?) can still be
called with dm_poll_bio(), and will trigger this warning.
> + bio->bi_end_io = saved_bi_end_io;
> +
> + hlist_for_each_entry_safe(io, next, &tmp, node) {
> + if (dm_poll_dm_io(io, flags)) {
> + hlist_del_init(&io->node);
> + dec_pending(io, 0);
> + }
> + }
> +
> + /* Not done, make sure at least one dm_io stores the .bi_end_io*/
> + if (!hlist_empty(&tmp)) {
> + io = hlist_entry(tmp.first, struct dm_io, node);
> + io->saved_bio_end_io = saved_bi_end_io;
> + hlist_move_list(&tmp, head);
> + return 0;> + }
> + return 1;
> +}
> +
> /*-----------------------------------------------------------------
> * An IDR is used to keep track of allocated minor numbers.
> *---------------------------------------------------------------*/
> @@ -3121,6 +3225,7 @@ static const struct pr_ops dm_pr_ops = {
>
> static const struct block_device_operations dm_blk_dops = {
> .submit_bio = dm_submit_bio,
> + .poll_bio = dm_poll_bio,
> .open = dm_blk_open,
> .release = dm_blk_close,
> .ioctl = dm_blk_ioctl,
>
--
Thanks,
Jeffle
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