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dm: add dm_submit_bio_remap interface

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Where possible, 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. When a target is updated to use dm_submit_bio_remap() they
must also set ti->accounts_remapped_io to true.

Use xchg() in start_io_acct(), as suggested by Mikulas, to ensure each
IO is only started once.  The xchg race only happens if
__send_duplicate_bios() sends multiple bios -- that case is reflected
via tio->is_duplicate_bio.  Given the niche nature of this race, it is
best to avoid any xchg performance penalty for normal IO.

For IO that was never submitted with dm_bio_submit_remap(), but the
target completes the clone with bio_endio, accounting is started then
ended and pending_io counter decremented.

Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer 2022-02-17 23:40:32 -05:00
parent e6fc9f62ce
commit 0fbb4d93b3
4 changed files with 118 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/md/dm-core.h
View File

@ -232,6 +232,8 @@ struct dm_io {
struct mapped_device *md;
struct bio *orig_bio;
blk_status_t status;
bool start_io_acct:1;
int was_accounted;
unsigned long start_time;
spinlock_t endio_lock;
struct dm_stats_aux stats_aux;

127
drivers/md/dm.c
View File

@ -518,14 +518,33 @@ static void dm_io_acct(bool end, struct mapped_device *md, struct bio *bio,
bio->bi_iter.bi_size = bi_size;
}
static void dm_start_io_acct(struct dm_io *io)
static void __dm_start_io_acct(struct dm_io *io, struct bio *bio)
{
dm_io_acct(false, io->md, io->orig_bio, io->start_time, &io->stats_aux);
dm_io_acct(false, io->md, bio, io->start_time, &io->stats_aux);
}
static void dm_end_io_acct(struct dm_io *io)
static void dm_start_io_acct(struct dm_io *io, struct bio *clone)
{
dm_io_acct(true, io->md, io->orig_bio, io->start_time, &io->stats_aux);
/* Must account IO to DM device in terms of orig_bio */
struct bio *bio = io->orig_bio;
/*
* Ensure IO accounting is only ever started once.
* Expect no possibility for race unless is_duplicate_bio.
*/
if (!clone || likely(!clone_to_tio(clone)->is_duplicate_bio)) {
if (WARN_ON(io->was_accounted))
return;
io->was_accounted = 1;
} else if (xchg(&io->was_accounted, 1) == 1)
return;
__dm_start_io_acct(io, bio);
}
static void dm_end_io_acct(struct dm_io *io, struct bio *bio)
{
dm_io_acct(true, io->md, bio, io->start_time, &io->stats_aux);
}
static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
@ -545,11 +564,13 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
io->status = 0;
atomic_set(&io->io_count, 1);
this_cpu_inc(*md->pending_io);
io->orig_bio = bio;
io->orig_bio = NULL;
io->md = md;
spin_lock_init(&io->endio_lock);
io->start_time = jiffies;
io->start_io_acct = false;
io->was_accounted = 0;
dm_stats_record_start(&md->stats, &io->stats_aux);
@ -849,7 +870,16 @@ void dm_io_dec_pending(struct dm_io *io, blk_status_t error)
}
io_error = io->status;
dm_end_io_acct(io);
if (io->was_accounted)
dm_end_io_acct(io, bio);
else if (!io_error) {
/*
* Must handle target that DM_MAPIO_SUBMITTED only to
* then bio_endio() rather than dm_submit_bio_remap()
*/
__dm_start_io_acct(io, bio);
dm_end_io_acct(io, bio);
}
free_io(io);
smp_wmb();
this_cpu_dec(*md->pending_io);
@ -1131,6 +1161,56 @@ void dm_accept_partial_bio(struct bio *bio, unsigned n_sectors)
}
EXPORT_SYMBOL_GPL(dm_accept_partial_bio);
static inline void __dm_submit_bio_remap(struct bio *clone,
dev_t dev, sector_t old_sector)
{
trace_block_bio_remap(clone, dev, old_sector);
submit_bio_noacct(clone);
}
/*
* @clone: clone bio that DM core passed to target's .map function
* @tgt_clone: clone of @clone bio that target needs submitted
* @from_wq: caller is a workqueue thread managed by DM target
*
* 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,
bool from_wq)
{
struct dm_target_io *tio = clone_to_tio(clone);
struct dm_io *io = tio->io;
/* establish bio that will get submitted */
if (!tgt_clone)
tgt_clone = clone;
/*
* Account io->origin_bio to DM dev on behalf of target
* that took ownership of IO with DM_MAPIO_SUBMITTED.
*/
if (!from_wq) {
/* Still in target's map function */
io->start_io_acct = true;
} else {
/*
* Called by another thread, managed by DM target,
* wait for dm_split_and_process_bio() to store
* io->orig_bio
*/
while (unlikely(!smp_load_acquire(&io->orig_bio)))
msleep(1);
dm_start_io_acct(io, clone);
}
__dm_submit_bio_remap(tgt_clone, disk_devt(io->md->disk),
tio->old_sector);
}
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);
@ -1157,9 +1237,7 @@ static void __map_bio(struct bio *clone)
clone->bi_end_io = clone_endio;
/*
* Map the clone. If r == 0 we don't need to do
* anything, the target has assumed ownership of
* this io.
* Map the clone.
*/
dm_io_inc_pending(io);
tio->old_sector = clone->bi_iter.bi_sector;
@ -1184,12 +1262,18 @@ 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)
io->start_io_acct = true;
break;
case DM_MAPIO_REMAPPED:
/* the bio has been remapped so dispatch it */
trace_block_bio_remap(clone, bio_dev(io->orig_bio),
/*
* the bio has been remapped so dispatch it, but defer
* dm_start_io_acct() until after possible bio_split().
*/
__dm_submit_bio_remap(clone, disk_devt(io->md->disk),
tio->old_sector);
submit_bio_noacct(clone);
io->start_io_acct = true;
break;
case DM_MAPIO_KILL:
case DM_MAPIO_REQUEUE:
@ -1404,7 +1488,7 @@ static void dm_split_and_process_bio(struct mapped_device *md,
struct dm_table *map, struct bio *bio)
{
struct clone_info ci;
struct bio *b;
struct bio *orig_bio = NULL;
int error = 0;
init_clone_info(&ci, md, map, bio);
@ -1426,15 +1510,18 @@ static void dm_split_and_process_bio(struct mapped_device *md,
* used by dm_end_io_acct() and for dm_io_dec_pending() to use for
* completion handling.
*/
b = bio_split(bio, bio_sectors(bio) - ci.sector_count,
GFP_NOIO, &md->queue->bio_split);
ci.io->orig_bio = b;
bio_chain(b, bio);
trace_block_split(b, bio->bi_iter.bi_sector);
orig_bio = bio_split(bio, bio_sectors(bio) - ci.sector_count,
GFP_NOIO, &md->queue->bio_split);
bio_chain(orig_bio, bio);
trace_block_split(orig_bio, bio->bi_iter.bi_sector);
submit_bio_noacct(bio);
out:
dm_start_io_acct(ci.io);
if (!orig_bio)
orig_bio = bio;
smp_store_release(&ci.io->orig_bio, orig_bio);
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));
}

7
include/linux/device-mapper.h
View File

@ -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, bool from_wq);
union map_info *dm_get_rq_mapinfo(struct request *rq);
#ifdef CONFIG_BLK_DEV_ZONED

4
include/uapi/linux/dm-ioctl.h
View File

@ -286,9 +286,9 @@ enum {
#define DM_DEV_SET_GEOMETRY _IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
#define DM_VERSION_MAJOR 4
#define DM_VERSION_MINOR 45
#define DM_VERSION_MINOR 46
#define DM_VERSION_PATCHLEVEL 0
#define DM_VERSION_EXTRA "-ioctl (2021-03-22)"
#define DM_VERSION_EXTRA "-ioctl (2022-02-22)"
/* Status bits */
#define DM_READONLY_FLAG (1 << 0) /* In/Out */