[dm-devel] [PATCH 10/14] dm: add dm_submit_bio_remap interface
Mike Snitzer
snitzer at redhat.com
Thu Feb 10 22:38:28 UTC 2022
Switch from early bio-based IO accounting (at the time DM clones each
incoming bio) to late IO accounting just before each remapped bio is
issued to underlying device via submit_bio_noacct().
Allows more precise bio-based IO accounting for DM targets that use
their own workqueues to perform additional processing of each bio in
conjunction with their DM_MAPIO_SUBMITTED return from their map
function.
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
---
drivers/md/dm-core.h | 1 +
drivers/md/dm.c | 93 +++++++++++++++++++++++++++++++++++++++----
include/linux/device-mapper.h | 7 ++++
3 files changed, 93 insertions(+), 8 deletions(-)
diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 8dd196aec130..3ecd6f294f53 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -230,6 +230,7 @@ struct dm_io {
atomic_t io_count;
struct bio *orig_bio;
unsigned long start_time;
+ unsigned long io_acct_time;
spinlock_t lock;
struct dm_stats_aux stats_aux;
/* last member of dm_target_io is 'struct bio' */
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8c0e96b8e1a5..ad512f40716e 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -485,21 +485,54 @@ u64 dm_start_time_ns_from_clone(struct bio *bio)
}
EXPORT_SYMBOL_GPL(dm_start_time_ns_from_clone);
-static void start_io_acct(struct dm_io *io)
+static void __start_io_acct(struct dm_io *io, struct bio *bio)
{
- struct bio *bio = io->orig_bio;
+ unsigned long flags;
- bio_start_io_acct_time(bio, io->start_time);
+ /* Ensure IO accounting is only ever started once */
+ spin_lock_irqsave(&io->lock, flags);
+ if (smp_load_acquire(&io->io_acct_time)) {
+ spin_unlock_irqrestore(&io->lock, flags);
+ return;
+ }
+ smp_store_release(&io->io_acct_time, jiffies);
+ spin_unlock_irqrestore(&io->lock, flags);
+ bio_start_io_acct_time(bio, io->start_time);
if (unlikely(dm_stats_used(&io->md->stats)))
dm_stats_account_io(&io->md->stats, bio_data_dir(bio),
bio->bi_iter.bi_sector, bio_sectors(bio),
false, 0, &io->stats_aux);
}
+static void start_io_acct(struct dm_io *io, struct bio *bio)
+{
+ /* Only start_io_acct() once for this IO */
+ if (smp_load_acquire(&io->io_acct_time))
+ return;
+
+ __start_io_acct(io, bio);
+}
+
+static void clone_and_start_io_acct(struct dm_io *io, struct bio *bio)
+{
+ struct bio io_acct_clone;
+
+ /* Only clone_and_start_io_acct() once for this IO */
+ if (smp_load_acquire(&io->io_acct_time))
+ return;
+
+ bio_init_clone(io->orig_bio->bi_bdev,
+ &io_acct_clone, bio, GFP_NOIO);
+ __start_io_acct(io, &io_acct_clone);
+}
+
static void end_io_acct(struct mapped_device *md, struct bio *bio,
unsigned long start_time, struct dm_stats_aux *stats_aux)
{
+ if (!start_time)
+ return;
+
bio_end_io_acct(bio, start_time);
if (unlikely(dm_stats_used(&md->stats)))
@@ -529,6 +562,7 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
spin_lock_init(&io->lock);
io->start_time = jiffies;
+ io->io_acct_time = 0;
return io;
}
@@ -818,7 +852,8 @@ void dm_io_dec_pending(struct dm_io *io, blk_status_t error)
}
io_error = io->status;
- start_time = io->start_time;
+ if (io->io_acct_time)
+ start_time = io->start_time;
stats_aux = io->stats_aux;
free_io(io);
end_io_acct(md, bio, start_time, &stats_aux);
@@ -1099,6 +1134,43 @@ void dm_accept_partial_bio(struct bio *bio, unsigned n_sectors)
}
EXPORT_SYMBOL_GPL(dm_accept_partial_bio);
+/*
+ * @clone: clone bio that DM core passed to target's .map function
+ * @tgt_clone: bio that target needs to submit (after DM_MAPIO_SUBMITTED)
+ *
+ * Targets should use this interface to submit bios they take
+ * ownership of when returning DM_MAPIO_SUBMITTED.
+ *
+ * Target should also enable ti->accounts_remapped_io
+ */
+void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone)
+{
+ struct dm_target_io *tio = clone_to_tio(clone);
+ struct dm_io *io = tio->io;
+ struct block_device *clone_bdev = clone->bi_bdev;
+
+ /* establish bio that will get submitted */
+ if (!tgt_clone)
+ tgt_clone = clone;
+
+ /*
+ * account IO to DM device in terms of clone's
+ * payload to avoid concern about late bio splitting.
+ * - clone will reflect any dm_accept_partial_bio()
+ * - any bio splitting is ultimately reflected in
+ * io->orig_bio so there is no IO imbalance in
+ * end_io_acct().
+ */
+ clone->bi_bdev = io->orig_bio->bi_bdev;
+ start_io_acct(io, clone);
+ clone->bi_bdev = clone_bdev;
+
+ trace_block_bio_remap(tgt_clone, bio_dev(io->orig_bio),
+ tio->old_sector);
+ submit_bio_noacct(tgt_clone);
+}
+EXPORT_SYMBOL_GPL(dm_submit_bio_remap);
+
static noinline void __set_swap_bios_limit(struct mapped_device *md, int latch)
{
mutex_lock(&md->swap_bios_lock);
@@ -1151,12 +1223,18 @@ static void __map_bio(struct bio *clone)
switch (r) {
case DM_MAPIO_SUBMITTED:
/* target has assumed ownership of this io */
+ if (!ti->accounts_remapped_io) {
+ /*
+ * Any split isn't reflected in io->orig_bio yet. And bio
+ * cannot be modified because target is submitting it.
+ * Clone bio and account IO to DM device.
+ */
+ clone_and_start_io_acct(io, clone);
+ }
break;
case DM_MAPIO_REMAPPED:
/* the bio has been remapped so dispatch it */
- trace_block_bio_remap(clone, bio_dev(io->orig_bio),
- tio->old_sector);
- submit_bio_noacct(clone);
+ dm_submit_bio_remap(clone, NULL);
break;
case DM_MAPIO_KILL:
case DM_MAPIO_REQUEUE:
@@ -1403,7 +1481,6 @@ static void dm_split_and_process_bio(struct mapped_device *md,
submit_bio_noacct(bio);
}
out:
- start_io_acct(ci.io);
/* drop the extra reference count */
dm_io_dec_pending(ci.io, errno_to_blk_status(error));
}
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index b26fecf6c8e8..a3e397155bc9 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -362,6 +362,12 @@ struct dm_target {
* zone append operations using regular writes.
*/
bool emulate_zone_append:1;
+
+ /*
+ * Set if the target will submit IO using dm_submit_bio_remap()
+ * after returning DM_MAPIO_SUBMITTED from its map function.
+ */
+ bool accounts_remapped_io:1;
};
void *dm_per_bio_data(struct bio *bio, size_t data_size);
@@ -465,6 +471,7 @@ int dm_suspended(struct dm_target *ti);
int dm_post_suspending(struct dm_target *ti);
int dm_noflush_suspending(struct dm_target *ti);
void dm_accept_partial_bio(struct bio *bio, unsigned n_sectors);
+void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone);
union map_info *dm_get_rq_mapinfo(struct request *rq);
#ifdef CONFIG_BLK_DEV_ZONED
--
2.15.0
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