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 <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Suggested-by: Yang Yang <yang.yang@vivo.com>
This commit is contained in:
Mikulas Patocka 2024-05-28 13:32:34 +02:00 committed by Mike Snitzer
parent cf546dd289
commit aaa53168cb
6 changed files with 61 additions and 12 deletions

View File

@ -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

View File

@ -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;

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@ -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))

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@ -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:

View File

@ -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);
}
}
/*

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@ -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);