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

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
......@@ -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 */
......
......@@ -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;
/*
* 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(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)
......
......@@ -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);
......
......@@ -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
......
......@@ -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,
};
......
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