[v6,2/2] dm: support bio polling

Message ID	20220307185303.71201-3-snitzer@redhat.com (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-block-owner@kernel.org> From: Mike Snitzer <snitzer@redhat.com> To: axboe@kernel.dk Cc: ming.lei@redhat.com, hch@lst.de, dm-devel@redhat.com, linux-block@vger.kernel.org Subject: [PATCH v6 2/2] dm: support bio polling Date: Mon, 7 Mar 2022 13:53:03 -0500 Message-Id: <20220307185303.71201-3-snitzer@redhat.com> In-Reply-To: <20220307185303.71201-1-snitzer@redhat.com> References: <20220307185303.71201-1-snitzer@redhat.com> Precedence: bulk
Series	block/dm: support bio polling \| expand [v6,0/2] block/dm: support bio polling [v6,1/2] block: add ->poll_bio to block_device_operations [v6,2/2] dm: support bio polling

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h index 8078b6c155ef..8cc03c0c262e 100644 --- a/drivers/md/dm-core.h +++ b/drivers/md/dm-core.h @@ -235,6 +235,8 @@ struct dm_io { bool start_io_acct:1; int was_accounted; unsigned long start_time; + void *data; + struct hlist_node node; spinlock_t endio_lock; struct dm_stats_aux stats_aux; /* last member of dm_target_io is 'struct bio' */ diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c index f4ed756ab391..c0be4f60b427 100644 --- a/drivers/md/dm-table.c +++ b/drivers/md/dm-table.c @@ -1481,6 +1481,14 @@ 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) +{ + struct request_queue *q = bdev_get_queue(dev->bdev); + + return !test_bit(QUEUE_FLAG_POLL, &q->queue_flags); +} + /* * type->iterate_devices() should be called when the sanity check needs to * iterate and check all underlying data devices. iterate_devices() will @@ -1531,6 +1539,11 @@ 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. @@ -2067,6 +2080,20 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q, dm_update_crypto_profile(q, t); disk_update_readahead(t->md->disk); + /* + * Check for request-based device is left 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); + } + return 0; } diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 454d39bc7745..d9111e17f0fc 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -40,6 +40,13 @@ #define DM_COOKIE_ENV_VAR_NAME "DM_COOKIE" #define DM_COOKIE_LENGTH 24 +/* + * For REQ_POLLED fs bio, this flag is set if we link mapped underlying + * dm_io into one list, and reuse bio->bi_private as the list head. Before + * ending this fs bio, we will recover its ->bi_private. + */ +#define REQ_DM_POLL_LIST REQ_DRV + static const char *_name = DM_NAME; static unsigned int major = 0; @@ -73,6 +80,7 @@ struct clone_info { struct dm_io *io; sector_t sector; unsigned sector_count; + bool submit_as_polled; }; #define DM_TARGET_IO_BIO_OFFSET (offsetof(struct dm_target_io, clone)) @@ -599,6 +607,9 @@ static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti, if (!clone) return NULL; + /* REQ_DM_POLL_LIST shouldn't be inherited */ + clone->bi_opf &= ~REQ_DM_POLL_LIST; + tio = clone_to_tio(clone); tio->inside_dm_io = false; } @@ -888,8 +899,15 @@ void dm_io_dec_pending(struct dm_io *io, blk_status_t error) if (unlikely(wq_has_sleeper(&md->wait))) wake_up(&md->wait); - if (io_error == BLK_STS_DM_REQUEUE) + if (io_error == BLK_STS_DM_REQUEUE) { + /* + * Upper layer won't help us poll split bio, io->orig_bio + * may only reflect a subset of the pre-split original, + * so clear REQ_POLLED in case of requeue + */ + bio->bi_opf &= ~REQ_POLLED; return; + } if (bio_is_flush_with_data(bio)) { /* @@ -1440,6 +1458,47 @@ static bool __process_abnormal_io(struct clone_info *ci, struct dm_target *ti, return true; } +/* + * Reuse ->bi_private as hlist head for storing all dm_io instances + * associated with this bio, and this bio's bi_private needs to be + * stored in dm_io->data before the reuse. + * + * bio->bi_private is owned by fs or upper layer, so block layer won't + * touch it after splitting. Meantime it won't be changed by anyone after + * bio is submitted. So this reuse is safe. + */ +static inline struct hlist_head *dm_get_bio_hlist_head(struct bio *bio) +{ + return (struct hlist_head *)&bio->bi_private; +} + +static void dm_queue_poll_io(struct bio *bio, struct dm_io *io) +{ + struct hlist_head *head = dm_get_bio_hlist_head(bio); + + if (!(bio->bi_opf & REQ_DM_POLL_LIST)) { + bio->bi_opf |= REQ_DM_POLL_LIST; + /* + * Save .bi_private into dm_io, so that we can reuse + * .bi_private as hlist head for storing dm_io list + */ + io->data = bio->bi_private; + + INIT_HLIST_HEAD(head); + + /* tell block layer to poll for completion */ + bio->bi_cookie = ~BLK_QC_T_NONE; + } else { + /* + * bio recursed due to split, reuse original poll list, + * and save bio->bi_private too. + */ + io->data = hlist_entry(head->first, struct dm_io, node)->data; + } + + hlist_add_head(&io->node, head); +} + /* * Select the correct strategy for processing a non-flush bio. */ @@ -1457,6 +1516,12 @@ static int __split_and_process_bio(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 (verified in dm_poll_dm_io) + */ + ci->submit_as_polled = ci->bio->bi_opf & REQ_POLLED; + len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count); clone = alloc_tio(ci, ti, 0, &len, GFP_NOIO); __map_bio(clone); @@ -1473,6 +1538,7 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md, ci->map = map; ci->io = alloc_io(md, bio); ci->bio = bio; + ci->submit_as_polled = false; ci->sector = bio->bi_iter.bi_sector; ci->sector_count = bio_sectors(bio); @@ -1522,8 +1588,17 @@ static void dm_split_and_process_bio(struct mapped_device *md, if (ci.io->start_io_acct) dm_start_io_acct(ci.io, NULL); - /* drop the extra reference count */ - dm_io_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_private, so that dm_poll_bio can poll them all. + */ + if (error || !ci.submit_as_polled) + dm_io_dec_pending(ci.io, errno_to_blk_status(error)); + else + dm_queue_poll_io(bio, ci.io); } static void dm_submit_bio(struct bio *bio) @@ -1558,6 +1633,67 @@ static void dm_submit_bio(struct bio *bio) dm_put_live_table(md, srcu_idx); } +static bool dm_poll_dm_io(struct dm_io *io, struct io_comp_batch *iob, + unsigned int flags) +{ + WARN_ON_ONCE(!io->tio.inside_dm_io); + + /* don't poll if the mapped io is done */ + if (atomic_read(&io->io_count) > 1) + bio_poll(&io->tio.clone, iob, flags); + + /* bio_poll holds the last reference */ + return atomic_read(&io->io_count) == 1; +} + +static int dm_poll_bio(struct bio *bio, struct io_comp_batch *iob, + unsigned int flags) +{ + struct hlist_head *head = dm_get_bio_hlist_head(bio); + struct hlist_head tmp = HLIST_HEAD_INIT; + struct hlist_node *next; + struct dm_io *io; + + /* Only poll normal bio which was marked as REQ_DM_POLL_LIST */ + if (!(bio->bi_opf & REQ_DM_POLL_LIST)) + return 0; + + WARN_ON_ONCE(hlist_empty(head)); + + hlist_move_list(head, &tmp); + + /* + * Restore .bi_private before possibly completing dm_io. + * + * bio_poll() is only possible once @bio has been completely + * submitted via submit_bio_noacct()'s depth-first submission. + * So there is no dm_queue_poll_io() race associated with + * clearing REQ_DM_POLL_LIST here. + */ + bio->bi_opf &= ~REQ_DM_POLL_LIST; + bio->bi_private = hlist_entry(tmp.first, struct dm_io, node)->data; + + hlist_for_each_entry_safe(io, next, &tmp, node) { + if (dm_poll_dm_io(io, iob, flags)) { + hlist_del_init(&io->node); + /* + * clone_endio() has already occurred, so passing + * error as 0 here doesn't override io->status + */ + dm_io_dec_pending(io, 0); + } + } + + /* Not done? */ + if (!hlist_empty(&tmp)) { + bio->bi_opf |= REQ_DM_POLL_LIST; + /* Reset bio->bi_private to dm_io list head */ + hlist_move_list(&tmp, head); + return 0; + } + return 1; +} + /*----------------------------------------------------------------- * An IDR is used to keep track of allocated minor numbers. *---------------------------------------------------------------*/ @@ -2983,6 +3119,7 @@ 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,

[v6,2/2] dm: support bio polling

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