From aaa53168cbcc486ca1927faac00bd99e81d4ff04 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 28 May 2024 13:32:34 +0200 Subject: [PATCH] dm: optimize flushes Device mapper sends flush bios to all the targets and the targets send it to the underlying device. That may be inefficient, for example if a table contains 10 linear targets pointing to the same physical device, then device mapper would send 10 flush bios to that device - despite the fact that only one bio would be sufficient. This commit optimizes the flush behavior. It introduces a per-target variable flush_bypasses_map - it is set when the target supports flush optimization - currently, the dm-linear and dm-stripe targets support it. When all the targets in a table have flush_bypasses_map, flush_bypasses_map on the table is set. __send_empty_flush tests if the table has flush_bypasses_map - and if it has, no flush bios are sent to the targets via the "map" method and the list dm_table->devices is iterated and the flush bios are sent to each member of the list. Signed-off-by: Mikulas Patocka Reviewed-by: Mike Snitzer Suggested-by: Yang Yang --- drivers/md/dm-core.h | 2 ++ drivers/md/dm-linear.c | 1 + drivers/md/dm-stripe.c | 1 + drivers/md/dm-table.c | 4 +++ drivers/md/dm.c | 50 ++++++++++++++++++++++++++--------- include/linux/device-mapper.h | 15 +++++++++++ 6 files changed, 61 insertions(+), 12 deletions(-) diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h index 14a44c0f8286..3637761f3585 100644 --- a/drivers/md/dm-core.h +++ b/drivers/md/dm-core.h @@ -206,6 +206,8 @@ struct dm_table { bool integrity_supported:1; bool singleton:1; + /* set if all the targets in the table have "flush_bypasses_map" set */ + bool flush_bypasses_map:1; /* * Indicates the rw permissions for the new logical device. This diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c index 2d3e186ca87e..49fb0f684193 100644 --- a/drivers/md/dm-linear.c +++ b/drivers/md/dm-linear.c @@ -62,6 +62,7 @@ static int linear_ctr(struct dm_target *ti, unsigned int argc, char **argv) ti->num_discard_bios = 1; ti->num_secure_erase_bios = 1; ti->num_write_zeroes_bios = 1; + ti->flush_bypasses_map = true; ti->private = lc; return 0; diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c index 16b93ae51d96..ec908cf8cfdc 100644 --- a/drivers/md/dm-stripe.c +++ b/drivers/md/dm-stripe.c @@ -157,6 +157,7 @@ static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv) ti->num_discard_bios = stripes; ti->num_secure_erase_bios = stripes; ti->num_write_zeroes_bios = stripes; + ti->flush_bypasses_map = true; sc->chunk_size = chunk_size; if (chunk_size & (chunk_size - 1)) diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c index 92d18dcdb3e9..33b7a1844ed4 100644 --- a/drivers/md/dm-table.c +++ b/drivers/md/dm-table.c @@ -160,6 +160,7 @@ int dm_table_create(struct dm_table **result, blk_mode_t mode, t->type = DM_TYPE_NONE; t->mode = mode; t->md = md; + t->flush_bypasses_map = true; *result = t; return 0; } @@ -748,6 +749,9 @@ int dm_table_add_target(struct dm_table *t, const char *type, if (ti->limit_swap_bios && !static_key_enabled(&swap_bios_enabled.key)) static_branch_enable(&swap_bios_enabled); + if (!ti->flush_bypasses_map) + t->flush_bypasses_map = false; + return 0; bad: diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 7d107ae06e1a..3763b2ce557b 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -645,7 +645,7 @@ static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti, /* Set default bdev, but target must bio_set_dev() before issuing IO */ clone->bi_bdev = md->disk->part0; - if (unlikely(ti->needs_bio_set_dev)) + if (likely(ti != NULL) && unlikely(ti->needs_bio_set_dev)) bio_set_dev(clone, md->disk->part0); if (len) { @@ -1107,7 +1107,7 @@ static void clone_endio(struct bio *bio) blk_status_t error = bio->bi_status; struct dm_target_io *tio = clone_to_tio(bio); struct dm_target *ti = tio->ti; - dm_endio_fn endio = ti->type->end_io; + dm_endio_fn endio = likely(ti != NULL) ? ti->type->end_io : NULL; struct dm_io *io = tio->io; struct mapped_device *md = io->md; @@ -1154,7 +1154,7 @@ static void clone_endio(struct bio *bio) } if (static_branch_unlikely(&swap_bios_enabled) && - unlikely(swap_bios_limit(ti, bio))) + likely(ti != NULL) && unlikely(swap_bios_limit(ti, bio))) up(&md->swap_bios_semaphore); free_tio(bio); @@ -1553,17 +1553,43 @@ static void __send_empty_flush(struct clone_info *ci) ci->sector_count = 0; ci->io->tio.clone.bi_iter.bi_size = 0; - for (unsigned int i = 0; i < t->num_targets; i++) { - unsigned int bios; - struct dm_target *ti = dm_table_get_target(t, i); + if (!t->flush_bypasses_map) { + for (unsigned int i = 0; i < t->num_targets; i++) { + unsigned int bios; + struct dm_target *ti = dm_table_get_target(t, i); - if (unlikely(ti->num_flush_bios == 0)) - continue; + if (unlikely(ti->num_flush_bios == 0)) + continue; - atomic_add(ti->num_flush_bios, &ci->io->io_count); - bios = __send_duplicate_bios(ci, ti, ti->num_flush_bios, - NULL, GFP_NOWAIT); - atomic_sub(ti->num_flush_bios - bios, &ci->io->io_count); + atomic_add(ti->num_flush_bios, &ci->io->io_count); + bios = __send_duplicate_bios(ci, ti, ti->num_flush_bios, + NULL, GFP_NOWAIT); + atomic_sub(ti->num_flush_bios - bios, &ci->io->io_count); + } + } else { + /* + * Note that there's no need to grab t->devices_lock here + * because the targets that support flush optimization don't + * modify the list of devices. + */ + struct list_head *devices = dm_table_get_devices(t); + unsigned int len = 0; + struct dm_dev_internal *dd; + list_for_each_entry(dd, devices, list) { + struct bio *clone; + /* + * Note that the structure dm_target_io is not + * associated with any target (because the device may be + * used by multiple targets), so we set tio->ti = NULL. + * We must check for NULL in the I/O processing path, to + * avoid NULL pointer dereference. + */ + clone = alloc_tio(ci, NULL, 0, &len, GFP_NOIO); + atomic_add(1, &ci->io->io_count); + bio_set_dev(clone, dd->dm_dev->bdev); + clone->bi_end_io = clone_endio; + dm_submit_bio_remap(clone, NULL); + } } /* diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h index 82b2195efaca..3611b230d0aa 100644 --- a/include/linux/device-mapper.h +++ b/include/linux/device-mapper.h @@ -397,6 +397,21 @@ struct dm_target { * bio_set_dev(). NOTE: ideally a target should _not_ need this. */ bool needs_bio_set_dev:1; + + /* + * Set if the target supports flush optimization. If all the targets in + * a table have flush_bypasses_map set, the dm core will not send + * flushes to the targets via a ->map method. It will iterate over + * dm_table->devices and send flushes to the devices directly. This + * optimization reduces the number of flushes being sent when multiple + * targets in a table use the same underlying device. + * + * This optimization may be enabled on targets that just pass the + * flushes to the underlying devices without performing any other + * actions on the flush request. Currently, dm-linear and dm-stripe + * support it. + */ + bool flush_bypasses_map:1; }; void *dm_per_bio_data(struct bio *bio, size_t data_size);