Commit a2309300 authored by Dennis Zhou's avatar Dennis Zhou Committed by David Sterba
Browse files

btrfs: calculate discard delay based on number of extents 



An earlier patch keeps track of discardable_extents. These are
undiscarded extents managed by the free space cache. Here, we will use
this to dynamically calculate the discard delay interval.

There are 3 rate to consider. The first is the target convergence rate,
the rate to discard all discardable_extents over the
BTRFS_DISCARD_TARGET_MSEC time frame. This is clamped by the lower
limit, the iops limit or BTRFS_DISCARD_MIN_DELAY (1ms), and the upper
limit, BTRFS_DISCARD_MAX_DELAY (1s). We reevaluate this delay every
transaction commit.

Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarDennis Zhou <dennis@kernel.org>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 5dc7c10b

fs/btrfs/ctree.h

+2 −0
Original line number Diff line number Diff line
@@ -468,6 +468,8 @@ struct btrfs_discard_ctl { 
	struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];

	atomic_t discardable_extents;

	atomic64_t discardable_bytes;

	unsigned long delay;

	u32 iops_limit;

};



/* delayed seq elem */

fs/btrfs/discard.c

+51 −4
Original line number Diff line number Diff line
@@ -15,6 +15,12 @@ 
#define BTRFS_DISCARD_DELAY		(120ULL * NSEC_PER_SEC)

#define BTRFS_DISCARD_UNUSED_DELAY	(10ULL * NSEC_PER_SEC)



/* Target completion latency of discarding all discardable extents */

#define BTRFS_DISCARD_TARGET_MSEC	(6 * 60 * 60UL * MSEC_PER_SEC)

#define BTRFS_DISCARD_MIN_DELAY_MSEC	(1UL)

#define BTRFS_DISCARD_MAX_DELAY_MSEC	(1000UL)

#define BTRFS_DISCARD_MAX_IOPS		(10U)



static struct list_head *get_discard_list(struct btrfs_discard_ctl *discard_ctl,

					  struct btrfs_block_group *block_group)

{
@@ -235,11 +241,17 @@ void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl, 


	block_group = find_next_block_group(discard_ctl, now);

	if (block_group) {

		u64 delay = 0;

		unsigned long delay = discard_ctl->delay;



		if (now < block_group->discard_eligible_time)

			delay = nsecs_to_jiffies(

				block_group->discard_eligible_time - now);

		/*

		 * This timeout is to hopefully prevent immediate discarding

		 * in a recently allocated block group.

		 */

		if (now < block_group->discard_eligible_time) {

			u64 bg_timeout = block_group->discard_eligible_time - now;



			delay = max(delay, nsecs_to_jiffies(bg_timeout));

		}



		mod_delayed_work(discard_ctl->discard_workers,

				 &discard_ctl->work, delay);
@@ -342,6 +354,39 @@ bool btrfs_run_discard_work(struct btrfs_discard_ctl *discard_ctl) 
		test_bit(BTRFS_FS_DISCARD_RUNNING, &fs_info->flags));

}



/**

 * btrfs_discard_calc_delay - recalculate the base delay

 * @discard_ctl: discard control

 *

 * Recalculate the base delay which is based off the total number of

 * discardable_extents.  Clamp this between the lower_limit (iops_limit or 1ms)

 * and the upper_limit (BTRFS_DISCARD_MAX_DELAY_MSEC).

 */

void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl)

{

	s32 discardable_extents;

	u32 iops_limit;

	unsigned long delay;

	unsigned long lower_limit = BTRFS_DISCARD_MIN_DELAY_MSEC;



	discardable_extents = atomic_read(&discard_ctl->discardable_extents);

	if (!discardable_extents)

		return;



	spin_lock(&discard_ctl->lock);



	iops_limit = READ_ONCE(discard_ctl->iops_limit);

	if (iops_limit)

		lower_limit = max_t(unsigned long, lower_limit,

				    MSEC_PER_SEC / iops_limit);



	delay = BTRFS_DISCARD_TARGET_MSEC / discardable_extents;

	delay = clamp(delay, lower_limit, BTRFS_DISCARD_MAX_DELAY_MSEC);

	discard_ctl->delay = msecs_to_jiffies(delay);



	spin_unlock(&discard_ctl->lock);

}



/**

 * btrfs_discard_update_discardable - propagate discard counters

 * @block_group: block_group of interest
@@ -464,6 +509,8 @@ void btrfs_discard_init(struct btrfs_fs_info *fs_info) 


	atomic_set(&discard_ctl->discardable_extents, 0);

	atomic64_set(&discard_ctl->discardable_bytes, 0);

	discard_ctl->delay = BTRFS_DISCARD_MAX_DELAY_MSEC;

	discard_ctl->iops_limit = BTRFS_DISCARD_MAX_IOPS;

}



void btrfs_discard_cleanup(struct btrfs_fs_info *fs_info)

fs/btrfs/discard.h

+1 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl, 
bool btrfs_run_discard_work(struct btrfs_discard_ctl *discard_ctl);



/* Update operations */

void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl);

void btrfs_discard_update_discardable(struct btrfs_block_group *block_group,

				      struct btrfs_free_space_ctl *ctl);

fs/btrfs/extent-tree.c

+3 −1
Original line number Diff line number Diff line
@@ -2935,8 +2935,10 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans) 
		cond_resched();

	}



	if (btrfs_test_opt(fs_info, DISCARD_ASYNC))

	if (btrfs_test_opt(fs_info, DISCARD_ASYNC)) {

		btrfs_discard_calc_delay(&fs_info->discard_ctl);

		btrfs_discard_schedule_work(&fs_info->discard_ctl, true);

	}



	/*

	 * Transaction is finished.  We don't need the lock anymore.  We

fs/btrfs/sysfs.c

+31 −0
Original line number Diff line number Diff line
@@ -366,9 +366,40 @@ static ssize_t btrfs_discardable_extents_show(struct kobject *kobj, 
}

BTRFS_ATTR(discard, discardable_extents, btrfs_discardable_extents_show);



static ssize_t btrfs_discard_iops_limit_show(struct kobject *kobj,

					     struct kobj_attribute *a,

					     char *buf)

{

	struct btrfs_fs_info *fs_info = discard_to_fs_info(kobj);



	return snprintf(buf, PAGE_SIZE, "%u\n",

			READ_ONCE(fs_info->discard_ctl.iops_limit));

}



static ssize_t btrfs_discard_iops_limit_store(struct kobject *kobj,

					      struct kobj_attribute *a,

					      const char *buf, size_t len)

{

	struct btrfs_fs_info *fs_info = discard_to_fs_info(kobj);

	struct btrfs_discard_ctl *discard_ctl = &fs_info->discard_ctl;

	u32 iops_limit;

	int ret;



	ret = kstrtou32(buf, 10, &iops_limit);

	if (ret)

		return -EINVAL;



	WRITE_ONCE(discard_ctl->iops_limit, iops_limit);



	return len;

}

BTRFS_ATTR_RW(discard, iops_limit, btrfs_discard_iops_limit_show,

	      btrfs_discard_iops_limit_store);



static const struct attribute *discard_debug_attrs[] = {

	BTRFS_ATTR_PTR(discard, discardable_bytes),

	BTRFS_ATTR_PTR(discard, discardable_extents),

	BTRFS_ATTR_PTR(discard, iops_limit),

	NULL,

};

CRA Git | Maintained and supported by SUSTech CRA and CCSE