[13/22] btrfs: calculate discard delay based on number of extents
diff mbox series

Message ID b87145b48a539223abc4611e3c279fb0bc750572.1576195673.git.dennis@kernel.org
State New
Headers show
Series
  • btrfs: async discard support
Related show

Commit Message

Dennis Zhou Dec. 14, 2019, 12:22 a.m. UTC
Use the number of discardable extents to help guide our discard delay
interval. This value is reevaluated every transaction commit.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/ctree.h       |  2 ++
 fs/btrfs/discard.c     | 53 ++++++++++++++++++++++++++++++++++++++----
 fs/btrfs/discard.h     |  1 +
 fs/btrfs/extent-tree.c |  4 +++-
 fs/btrfs/sysfs.c       | 31 ++++++++++++++++++++++++
 5 files changed, 86 insertions(+), 5 deletions(-)

Comments

David Sterba Dec. 30, 2019, 4:50 p.m. UTC | #1
On Fri, Dec 13, 2019 at 04:22:22PM -0800, Dennis Zhou wrote:
> Use the number of discardable extents to help guide our discard delay
> interval. This value is reevaluated every transaction commit.

This is too short compared to the added code, please enhance it eg. by
briefly describing what values are tracked and how are they related
together.

> Signed-off-by: Dennis Zhou <dennis@kernel.org>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/ctree.h       |  2 ++
>  fs/btrfs/discard.c     | 53 ++++++++++++++++++++++++++++++++++++++----
>  fs/btrfs/discard.h     |  1 +
>  fs/btrfs/extent-tree.c |  4 +++-
>  fs/btrfs/sysfs.c       | 31 ++++++++++++++++++++++++
>  5 files changed, 86 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 18df0e40a282..98979566e281 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -469,6 +469,8 @@ struct btrfs_discard_ctl {
>  	struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
>  	atomic_t discardable_extents;
>  	atomic64_t discardable_bytes;

There are some type mismatches for the two:

> +	u32 delay;
> +	u32 iops_limit;

unsigned for iops

>  };
>  
>  /* delayed seq elem */
> diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
> index e8c2623617fd..160713e04d0c 100644
> --- a/fs/btrfs/discard.c
> +++ b/fs/btrfs/discard.c
> @@ -15,6 +15,11 @@
>  #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_MAX_DELAY		(10000UL)
> +#define BTRFS_DISCARD_MAX_IOPS		(10UL)

All unsigned longs

> +
>  static struct list_head *get_discard_list(struct btrfs_discard_ctl *discard_ctl,
>  					  struct btrfs_block_group *block_group)
>  {
> @@ -239,11 +244,18 @@ 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;
> +		u32 delay = discard_ctl->delay;
> +
> +		/*
> +		 * 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);
>  
> -		if (now < block_group->discard_eligible_time)
> -			delay = nsecs_to_jiffies(
> -				block_group->discard_eligible_time - now);
> +			delay = max_t(u64, delay, nsecs_to_jiffies(bg_timeout));

delay is u32, nsecs_to_jiffies returns unsigned long, so delay should be
also unsigned long everywhere.

> +		}
>  
>  		mod_delayed_work(discard_ctl->discard_workers,
>  				 &discard_ctl->work,
> @@ -348,6 +360,37 @@ 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 with the iops_limit and
> + * BTRFS_DISCARD_MAX_DELAY.
> + */
> +void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl)
> +{
> +	s32 discardable_extents =
> +		atomic_read(&discard_ctl->discardable_extents);
> +	s32 iops_limit;

signed for iops

> +	unsigned long delay;
> +
> +	if (!discardable_extents)
> +		return;
> +
> +	spin_lock(&discard_ctl->lock);
> +
> +	iops_limit = READ_ONCE(discard_ctl->iops_limit);

unsigned -> signed

> +	if (iops_limit)
> +		iops_limit = MSEC_PER_SEC / iops_limit;
> +
> +	delay = BTRFS_DISCARD_TARGET_MSEC / discardable_extents;
> +	delay = clamp_t(s32, delay, iops_limit, BTRFS_DISCARD_MAX_DELAY);
> +	discard_ctl->delay = msecs_to_jiffies(delay);

unsigned long -> u32

> +
> +	spin_unlock(&discard_ctl->lock);
> +}
> +
>  /**
>   * btrfs_discard_update_discardable - propagate discard counters
>   * @block_group: block_group of interest
> @@ -476,6 +519,8 @@ 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;
> +	discard_ctl->iops_limit = BTRFS_DISCARD_MAX_IOPS;
>  }
>  
>  void btrfs_discard_cleanup(struct btrfs_fs_info *fs_info)
> diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
> index 7e3680dd82ce..3ed6855e24da 100644
> --- a/fs/btrfs/discard.h
> +++ b/fs/btrfs/discard.h
> @@ -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);
>  
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 2c12366cfde5..0163fdd59f8f 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -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
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index e799d4488d72..79139b4b4f0a 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -344,6 +344,36 @@ static const struct attribute_group btrfs_static_feature_attr_group = {
>   */
>  #define discard_to_fs_info(_kobj)	to_fs_info((_kobj)->parent->parent)
>  
> +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 ssize_t btrfs_discardable_extents_show(struct kobject *kobj,
>  					      struct kobj_attribute *a,
>  					      char *buf)
> @@ -367,6 +397,7 @@ static ssize_t btrfs_discardable_bytes_show(struct kobject *kobj,
>  BTRFS_ATTR(discard, discardable_bytes, btrfs_discardable_bytes_show);
>  
>  static const struct attribute *discard_debug_attrs[] = {
> +	BTRFS_ATTR_PTR(discard, iops_limit),
>  	BTRFS_ATTR_PTR(discard, discardable_extents),
>  	BTRFS_ATTR_PTR(discard, discardable_bytes),
>  	NULL,
> -- 
> 2.17.1
Dennis Zhou Jan. 2, 2020, 4:45 p.m. UTC | #2
On Mon, Dec 30, 2019 at 05:50:43PM +0100, David Sterba wrote:
> On Fri, Dec 13, 2019 at 04:22:22PM -0800, Dennis Zhou wrote:
> > Use the number of discardable extents to help guide our discard delay
> > interval. This value is reevaluated every transaction commit.
> 
> This is too short compared to the added code, please enhance it eg. by
> briefly describing what values are tracked and how are they related
> together.
> 

Done.

> > Signed-off-by: Dennis Zhou <dennis@kernel.org>
> > Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> > ---
> >  fs/btrfs/ctree.h       |  2 ++
> >  fs/btrfs/discard.c     | 53 ++++++++++++++++++++++++++++++++++++++----
> >  fs/btrfs/discard.h     |  1 +
> >  fs/btrfs/extent-tree.c |  4 +++-
> >  fs/btrfs/sysfs.c       | 31 ++++++++++++++++++++++++
> >  5 files changed, 86 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > index 18df0e40a282..98979566e281 100644
> > --- a/fs/btrfs/ctree.h
> > +++ b/fs/btrfs/ctree.h
> > @@ -469,6 +469,8 @@ struct btrfs_discard_ctl {
> >  	struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
> >  	atomic_t discardable_extents;
> >  	atomic64_t discardable_bytes;
> 
> There are some type mismatches for the two:
> 
> > +	u32 delay;
> > +	u32 iops_limit;
> 
> unsigned for iops

I switched iops_limit to unsigned and delay to unsigned long.

> 
> >  };
> >  
> >  /* delayed seq elem */
> > diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
> > index e8c2623617fd..160713e04d0c 100644
> > --- a/fs/btrfs/discard.c
> > +++ b/fs/btrfs/discard.c
> > @@ -15,6 +15,11 @@
> >  #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_MAX_DELAY		(10000UL)
> > +#define BTRFS_DISCARD_MAX_IOPS		(10UL)
> 
> All unsigned longs
> 

I've switched BTRFS_DISCARD_MAX_IOPS to 10U and lowered the max delay to
be 1s from our previous conversation.

> > +
> >  static struct list_head *get_discard_list(struct btrfs_discard_ctl *discard_ctl,
> >  					  struct btrfs_block_group *block_group)
> >  {
> > @@ -239,11 +244,18 @@ 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;
> > +		u32 delay = discard_ctl->delay;
> > +
> > +		/*
> > +		 * 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);
> >  
> > -		if (now < block_group->discard_eligible_time)
> > -			delay = nsecs_to_jiffies(
> > -				block_group->discard_eligible_time - now);
> > +			delay = max_t(u64, delay, nsecs_to_jiffies(bg_timeout));
> 
> delay is u32, nsecs_to_jiffies returns unsigned long, so delay should be
> also unsigned long everywhere.
> 
> > +		}
> >  
> >  		mod_delayed_work(discard_ctl->discard_workers,
> >  				 &discard_ctl->work,
> > @@ -348,6 +360,37 @@ 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 with the iops_limit and
> > + * BTRFS_DISCARD_MAX_DELAY.
> > + */
> > +void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl)
> > +{
> > +	s32 discardable_extents =
> > +		atomic_read(&discard_ctl->discardable_extents);
> > +	s32 iops_limit;
> 
> signed for iops
> 
> > +	unsigned long delay;
> > +
> > +	if (!discardable_extents)
> > +		return;
> > +
> > +	spin_lock(&discard_ctl->lock);
> > +
> > +	iops_limit = READ_ONCE(discard_ctl->iops_limit);
> 
> unsigned -> signed
> 
> > +	if (iops_limit)
> > +		iops_limit = MSEC_PER_SEC / iops_limit;
> > +
> > +	delay = BTRFS_DISCARD_TARGET_MSEC / discardable_extents;
> > +	delay = clamp_t(s32, delay, iops_limit, BTRFS_DISCARD_MAX_DELAY);
> > +	discard_ctl->delay = msecs_to_jiffies(delay);
> 
> unsigned long -> u32
> 
> > +
> > +	spin_unlock(&discard_ctl->lock);
> > +}
> > +
> >  /**
> >   * btrfs_discard_update_discardable - propagate discard counters
> >   * @block_group: block_group of interest
> > @@ -476,6 +519,8 @@ 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;
> > +	discard_ctl->iops_limit = BTRFS_DISCARD_MAX_IOPS;
> >  }
> >  
> >  void btrfs_discard_cleanup(struct btrfs_fs_info *fs_info)
> > diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
> > index 7e3680dd82ce..3ed6855e24da 100644
> > --- a/fs/btrfs/discard.h
> > +++ b/fs/btrfs/discard.h
> > @@ -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);
> >  
> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> > index 2c12366cfde5..0163fdd59f8f 100644
> > --- a/fs/btrfs/extent-tree.c
> > +++ b/fs/btrfs/extent-tree.c
> > @@ -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
> > diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> > index e799d4488d72..79139b4b4f0a 100644
> > --- a/fs/btrfs/sysfs.c
> > +++ b/fs/btrfs/sysfs.c
> > @@ -344,6 +344,36 @@ static const struct attribute_group btrfs_static_feature_attr_group = {
> >   */
> >  #define discard_to_fs_info(_kobj)	to_fs_info((_kobj)->parent->parent)
> >  
> > +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 ssize_t btrfs_discardable_extents_show(struct kobject *kobj,
> >  					      struct kobj_attribute *a,
> >  					      char *buf)
> > @@ -367,6 +397,7 @@ static ssize_t btrfs_discardable_bytes_show(struct kobject *kobj,
> >  BTRFS_ATTR(discard, discardable_bytes, btrfs_discardable_bytes_show);
> >  
> >  static const struct attribute *discard_debug_attrs[] = {
> > +	BTRFS_ATTR_PTR(discard, iops_limit),
> >  	BTRFS_ATTR_PTR(discard, discardable_extents),
> >  	BTRFS_ATTR_PTR(discard, discardable_bytes),
> >  	NULL,
> > -- 
> > 2.17.1

Patch
diff mbox series

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 18df0e40a282..98979566e281 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -469,6 +469,8 @@  struct btrfs_discard_ctl {
 	struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
 	atomic_t discardable_extents;
 	atomic64_t discardable_bytes;
+	u32 delay;
+	u32 iops_limit;
 };
 
 /* delayed seq elem */
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index e8c2623617fd..160713e04d0c 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -15,6 +15,11 @@ 
 #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_MAX_DELAY		(10000UL)
+#define BTRFS_DISCARD_MAX_IOPS		(10UL)
+
 static struct list_head *get_discard_list(struct btrfs_discard_ctl *discard_ctl,
 					  struct btrfs_block_group *block_group)
 {
@@ -239,11 +244,18 @@  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;
+		u32 delay = discard_ctl->delay;
+
+		/*
+		 * 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);
 
-		if (now < block_group->discard_eligible_time)
-			delay = nsecs_to_jiffies(
-				block_group->discard_eligible_time - now);
+			delay = max_t(u64, delay, nsecs_to_jiffies(bg_timeout));
+		}
 
 		mod_delayed_work(discard_ctl->discard_workers,
 				 &discard_ctl->work,
@@ -348,6 +360,37 @@  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 with the iops_limit and
+ * BTRFS_DISCARD_MAX_DELAY.
+ */
+void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl)
+{
+	s32 discardable_extents =
+		atomic_read(&discard_ctl->discardable_extents);
+	s32 iops_limit;
+	unsigned long delay;
+
+	if (!discardable_extents)
+		return;
+
+	spin_lock(&discard_ctl->lock);
+
+	iops_limit = READ_ONCE(discard_ctl->iops_limit);
+	if (iops_limit)
+		iops_limit = MSEC_PER_SEC / iops_limit;
+
+	delay = BTRFS_DISCARD_TARGET_MSEC / discardable_extents;
+	delay = clamp_t(s32, delay, iops_limit, BTRFS_DISCARD_MAX_DELAY);
+	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
@@ -476,6 +519,8 @@  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;
+	discard_ctl->iops_limit = BTRFS_DISCARD_MAX_IOPS;
 }
 
 void btrfs_discard_cleanup(struct btrfs_fs_info *fs_info)
diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
index 7e3680dd82ce..3ed6855e24da 100644
--- a/fs/btrfs/discard.h
+++ b/fs/btrfs/discard.h
@@ -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);
 
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 2c12366cfde5..0163fdd59f8f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -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
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index e799d4488d72..79139b4b4f0a 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -344,6 +344,36 @@  static const struct attribute_group btrfs_static_feature_attr_group = {
  */
 #define discard_to_fs_info(_kobj)	to_fs_info((_kobj)->parent->parent)
 
+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 ssize_t btrfs_discardable_extents_show(struct kobject *kobj,
 					      struct kobj_attribute *a,
 					      char *buf)
@@ -367,6 +397,7 @@  static ssize_t btrfs_discardable_bytes_show(struct kobject *kobj,
 BTRFS_ATTR(discard, discardable_bytes, btrfs_discardable_bytes_show);
 
 static const struct attribute *discard_debug_attrs[] = {
+	BTRFS_ATTR_PTR(discard, iops_limit),
 	BTRFS_ATTR_PTR(discard, discardable_extents),
 	BTRFS_ATTR_PTR(discard, discardable_bytes),
 	NULL,