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dm: improve dm_io reference counting

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Currently each dm_io's reference counter is grabbed before calling
__map_bio(), this way isn't efficient since we can move this grabbing
to initialization time inside alloc_io().

Meantime it becomes typical async io reference counter model: one is
for submission side, the other is for completion side, and the io won't
be completed until both sides are done.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Ming Lei 2022-04-12 16:56:15 +08:00 committed by Mike Snitzer
parent 2e803cd99b
commit 0f14d60a02
1 changed files with 39 additions and 14 deletions
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53
drivers/md/dm.c
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@ -590,7 +590,9 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
io = container_of(tio, struct dm_io, tio);
io->magic = DM_IO_MAGIC;
io->status = BLK_STS_OK;
atomic_set(&io->io_count, 1);
/* one ref is for submission, the other is for completion */
atomic_set(&io->io_count, 2);
this_cpu_inc(*md->pending_io);
io->orig_bio = bio;
io->md = md;
@ -955,11 +957,6 @@ static void dm_io_complete(struct dm_io *io)
}
}
static void dm_io_inc_pending(struct dm_io *io)
{
atomic_inc(&io->io_count);
}
/*
* Decrements the number of outstanding ios that a bio has been
* cloned into, completing the original io if necc.
@ -1316,7 +1313,6 @@ static void __map_bio(struct bio *clone)
/*
* Map the clone.
*/
dm_io_inc_pending(io);
tio->old_sector = clone->bi_iter.bi_sector;
if (static_branch_unlikely(&swap_bios_enabled) &&
@ -1426,11 +1422,12 @@ static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,
}
}
static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
static int __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
unsigned num_bios, unsigned *len)
{
struct bio_list blist = BIO_EMPTY_LIST;
struct bio *clone;
int ret = 0;
switch (num_bios) {
case 0:
@ -1440,6 +1437,7 @@ static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
setup_split_accounting(ci, *len);
clone = alloc_tio(ci, ti, 0, len, GFP_NOIO);
__map_bio(clone);
ret = 1;
break;
default:
/* dm_accept_partial_bio() is not supported with shared tio->len_ptr */
@ -1447,9 +1445,12 @@ static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
while ((clone = bio_list_pop(&blist))) {
dm_tio_set_flag(clone_to_tio(clone), DM_TIO_IS_DUPLICATE_BIO);
__map_bio(clone);
ret += 1;
}
break;
}
return ret;
}
static void __send_empty_flush(struct clone_info *ci)
@ -1470,8 +1471,19 @@ static void __send_empty_flush(struct clone_info *ci)
ci->sector_count = 0;
ci->io->tio.clone.bi_iter.bi_size = 0;
while ((ti = dm_table_get_target(ci->map, target_nr++)))
__send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL);
while ((ti = dm_table_get_target(ci->map, target_nr++))) {
int bios;
atomic_add(ti->num_flush_bios, &ci->io->io_count);
bios = __send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL);
atomic_sub(ti->num_flush_bios - bios, &ci->io->io_count);
}
/*
* alloc_io() takes one extra reference for submission, so the
* reference won't reach 0 without the following subtraction
*/
atomic_sub(1, &ci->io->io_count);
bio_uninit(ci->bio);
}
@ -1480,11 +1492,18 @@ static void __send_changing_extent_only(struct clone_info *ci, struct dm_target
unsigned num_bios)
{
unsigned len;
int bios;
len = min_t(sector_t, ci->sector_count,
max_io_len_target_boundary(ti, dm_target_offset(ti, ci->sector)));
__send_duplicate_bios(ci, ti, num_bios, &len);
atomic_add(num_bios, &ci->io->io_count);
bios = __send_duplicate_bios(ci, ti, num_bios, &len);
/*
* alloc_io() takes one extra reference for submission, so the
* reference won't reach 0 without the following (+1) subtraction
*/
atomic_sub(num_bios - bios + 1, &ci->io->io_count);
ci->sector += len;
ci->sector_count -= len;
@ -1669,9 +1688,15 @@ out:
* Add every dm_io instance into the hlist_head which is stored in
* bio->bi_private, so that dm_poll_bio can poll them all.
*/
if (error || !ci.submit_as_polled)
dm_io_dec_pending(ci.io, error);
else
if (error || !ci.submit_as_polled) {
/*
* In case of submission failure, the extra reference for
* submitting io isn't consumed yet
*/
if (error)
atomic_dec(&io->io_count);
dm_io_dec_pending(io, error);
} else
dm_queue_poll_io(bio, io);
}