Commit 4a2fe296 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm: enhance alloc_multiple_bios() to be more versatile 



alloc_multiple_bios() has the useful ability to try allocating bios
with GFP_NOWAIT but will fallback to using GFP_NOIO.  The callers
service both empty flush bios and abnormal bios (e.g. discard).

alloc_multiple_bios() enhancements offered in this commit:
- don't require table_devices_lock if num_bios = 1
- allow caller to pass GFP_NOWAIT to do usual GFP_NOWAIT with GFP_NOIO
  fallback
- allow caller to pass GFP_NOIO to _only_ allocate using GFP_NOIO

Flush bios with data may be issued to DM with REQ_NOWAIT, as such it
makes sense to attempt servicing them with GFP_NOWAIT allocations.

But abnormal IO should never be issued using REQ_NOWAIT (if that
changes in the future that's fine, but no sense supporting it now).

While at it, rename __send_changing_extent_only() to
__send_abnormal_io().

[Thanks to both Ming and Mikulas for help with translating known
possible IO scenarios to requirements.]

Suggested-by: default avatarMing Lei <ming.lei@redhat.com>
Suggested-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
parent 34dbaa88

drivers/md/dm.c

+34 −34
Original line number Diff line number Diff line
@@ -1478,15 +1478,15 @@ static void setup_split_accounting(struct clone_info *ci, unsigned int len) 


static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,

				struct dm_target *ti, unsigned int num_bios,

				unsigned *len)

				unsigned *len, gfp_t gfp_flag)

{

	struct bio *bio;

	int try;

	int try = (gfp_flag & GFP_NOWAIT) ? 0 : 1;



	for (try = 0; try < 2; try++) {

	for (; try < 2; try++) {

		int bio_nr;



		if (try)

		if (try && num_bios > 1)

			mutex_lock(&ci->io->md->table_devices_lock);

		for (bio_nr = 0; bio_nr < num_bios; bio_nr++) {

			bio = alloc_tio(ci, ti, bio_nr, len,
@@ -1496,7 +1496,7 @@ static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci, 


			bio_list_add(blist, bio);

		}

		if (try)

		if (try && num_bios > 1)

			mutex_unlock(&ci->io->md->table_devices_lock);

		if (bio_nr == num_bios)

			return;
@@ -1507,34 +1507,31 @@ static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci, 
}



static unsigned int __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,

					  unsigned int num_bios, unsigned int *len)

					  unsigned int num_bios, unsigned int *len,

					  gfp_t gfp_flag)

{

	struct bio_list blist = BIO_EMPTY_LIST;

	struct bio *clone;

	unsigned int ret = 0;



	switch (num_bios) {

	case 0:

		break;

	case 1:

		if (len)

			setup_split_accounting(ci, *len);

		clone = alloc_tio(ci, ti, 0, len, GFP_NOIO);

		__map_bio(clone);

		ret = 1;

		break;

	default:

	if (WARN_ON_ONCE(num_bios == 0)) /* num_bios = 0 is a bug in caller */

		return 0;



	/* dm_accept_partial_bio() is not supported with shared tio->len_ptr */

	if (len)

		setup_split_accounting(ci, *len);

		/* dm_accept_partial_bio() is not supported with shared tio->len_ptr */

		alloc_multiple_bios(&blist, ci, ti, num_bios, len);



	/*

	 * Using alloc_multiple_bios(), even if num_bios is 1, to consistently

	 * support allocating using GFP_NOWAIT with GFP_NOIO fallback.

	 */

	alloc_multiple_bios(&blist, ci, ti, num_bios, len, gfp_flag);

	while ((clone = bio_list_pop(&blist))) {

		if (num_bios > 1)

			dm_tio_set_flag(clone_to_tio(clone), DM_TIO_IS_DUPLICATE_BIO);

		__map_bio(clone);

		ret += 1;

	}

		break;

	}



	return ret;

}
@@ -1560,8 +1557,12 @@ static void __send_empty_flush(struct clone_info *ci) 
		unsigned int bios;

		struct dm_target *ti = dm_table_get_target(t, i);



		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);

		bios = __send_duplicate_bios(ci, ti, ti->num_flush_bios,

					     NULL, GFP_NOWAIT);

		atomic_sub(ti->num_flush_bios - bios, &ci->io->io_count);

	}
@@ -1574,9 +1575,8 @@ static void __send_empty_flush(struct clone_info *ci) 
	bio_uninit(ci->bio);

}



static void __send_changing_extent_only(struct clone_info *ci, struct dm_target *ti,

					unsigned int num_bios,

					unsigned int max_granularity,

static void __send_abnormal_io(struct clone_info *ci, struct dm_target *ti,

			       unsigned int num_bios, unsigned int max_granularity,

			       unsigned int max_sectors)

{

	unsigned int len, bios;
@@ -1585,7 +1585,7 @@ static void __send_changing_extent_only(struct clone_info *ci, struct dm_target 
		    __max_io_len(ti, ci->sector, max_granularity, max_sectors));



	atomic_add(num_bios, &ci->io->io_count);

	bios = __send_duplicate_bios(ci, ti, num_bios, &len);

	bios = __send_duplicate_bios(ci, ti, num_bios, &len, GFP_NOIO);

	/*

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

	 * reference won't reach 0 without the following (+1) subtraction
@@ -1654,8 +1654,8 @@ static blk_status_t __process_abnormal_io(struct clone_info *ci, 
	if (unlikely(!num_bios))

		return BLK_STS_NOTSUPP;



	__send_changing_extent_only(ci, ti, num_bios,

				    max_granularity, max_sectors);

	__send_abnormal_io(ci, ti, num_bios, max_granularity, max_sectors);



	return BLK_STS_OK;

}