Commit aaa53168 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Reviewed-by: default avatarMike Snitzer <snitzer@kernel.org>
Suggested-by: default avatarYang Yang <yang.yang@vivo.com>
parent cf546dd2

drivers/md/dm-core.h

+2 −0
Original line number Diff line number Diff line
@@ -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

drivers/md/dm-linear.c

+1 −0
Original line number Diff line number Diff line
@@ -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;

drivers/md/dm-stripe.c

+1 −0
Original line number Diff line number Diff line
@@ -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))

drivers/md/dm-table.c

+4 −0
Original line number Diff line number Diff line
@@ -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:

drivers/md/dm.c

+38 −12
Original line number Diff line number Diff line
@@ -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);
@@ -1553,6 +1553,7 @@ static void __send_empty_flush(struct clone_info *ci) 
	ci->sector_count = 0;

	ci->io->tio.clone.bi_iter.bi_size = 0;



	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);
@@ -1565,6 +1566,31 @@ static void __send_empty_flush(struct clone_info *ci) 
						     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);

		}

	}



	/*

	 * alloc_io() takes one extra reference for submission, so the