[PATCH 02/12] btrfs: add bps discard rate limit for async discard

Dennis Zhou
2020-01-02T21:26:55Z

Provide the ability to rate limit based on kbps in addition to iops as
additional guides for the target discard rate. The delay used ends up
being max(kbps_delay, iops_delay).

Signed-off-by: Dennis Zhou <dennis@kernel.org>
---
fs/btrfs/ctree.h | 2 ++
fs/btrfs/discard.c | 23 +++++++++++++++++++++--
fs/btrfs/sysfs.c | 31 +++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index c73bbc7e4491..2485cf94b628 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -466,10 +466,12 @@ struct btrfs_discard_ctl {
spinlock_t lock;
struct btrfs_block_group *block_group;
struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
+ u64 prev_discard;
atomic_t discardable_extents;
atomic64_t discardable_bytes;
unsigned long delay;
unsigned iops_limit;
+ u32 kbps_limit;
};

/* delayed seq elem */
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index abcc3b2189d1..eb148ca9a508 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -4,6 +4,7 @@
#include <linux/kernel.h>
#include <linux/ktime.h>
#include <linux/list.h>
+#include <linux/math64.h>
#include <linux/sizes.h>
#include <linux/workqueue.h>
#include "ctree.h"
@@ -222,8 +223,8 @@ void btrfs_discard_queue_work(struct btrfs_discard_ctl *discard_ctl,
* @override: override the current timer
*
* Discards are issued by a delayed workqueue item. @override is used to
- * update the current delay as the baseline delay interview is reevaluated
- * on transaction commit. This is also maxed with any other rate limit.
+ * update the current delay as the baseline delay interval is reevaluated on
+ * transaction commit. This is also maxed with any other rate limit.
*/
void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
bool override)
@@ -242,6 +243,20 @@ void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
block_group = find_next_block_group(discard_ctl, now);
if (block_group) {
unsigned long delay = discard_ctl->delay;
+ u32 kbps_limit = READ_ONCE(discard_ctl->kbps_limit);
+
+ /*
+ * A single delayed workqueue item is responsible for
+ * discarding, so we can manage the bytes rate limit by keeping
+ * track of the previous discard.
+ */
+ if (kbps_limit && discard_ctl->prev_discard) {
+ u64 bps_limit = ((u64)kbps_limit) * SZ_1K;
+ u64 bps_delay = div64_u64(discard_ctl->prev_discard *
+ MSEC_PER_SEC, bps_limit);
+
+ delay = max(delay, msecs_to_jiffies(bps_delay));
+ }

/*
* This timeout is to hopefully prevent immediate discarding
@@ -317,6 +332,8 @@ static void btrfs_discard_workfn(struct work_struct *work)
btrfs_block_group_end(block_group),
0, true);

+ discard_ctl->prev_discard = trimmed;
+
/* Determine next steps for a block_group */
if (block_group->discard_cursor >= btrfs_block_group_end(block_group)) {
if (discard_state == BTRFS_DISCARD_BITMAPS) {
@@ -507,10 +524,12 @@ void btrfs_discard_init(struct btrfs_fs_info *fs_info)
for (i = 0; i < BTRFS_NR_DISCARD_LISTS; i++)
INIT_LIST_HEAD(&discard_ctl->discard_list[i]);

+ discard_ctl->prev_discard = 0;
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;
+ discard_ctl->kbps_limit = 0;
}

void btrfs_discard_cleanup(struct btrfs_fs_info *fs_info)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index e175aaf7a1e6..39b59f368f06 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -374,6 +374,36 @@ static ssize_t btrfs_discard_iops_limit_store(struct kobject *kobj,
BTRFS_ATTR_RW(discard, iops_limit, btrfs_discard_iops_limit_show,
btrfs_discard_iops_limit_store);

+static ssize_t btrfs_discard_kbps_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.kbps_limit));
+}
+
+static ssize_t btrfs_discard_kbps_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 kbps_limit;
+ int ret;
+
+ ret = kstrtou32(buf, 10, &kbps_limit);
+ if (ret)
+ return -EINVAL;
+
+ WRITE_ONCE(discard_ctl->kbps_limit, kbps_limit);
+
+ return len;
+}
+BTRFS_ATTR_RW(discard, kbps_limit, btrfs_discard_kbps_limit_show,
+ btrfs_discard_kbps_limit_store);
+
static ssize_t btrfs_discardable_extents_show(struct kobject *kobj,
struct kobj_attribute *a,
char *buf)
@@ -398,6 +428,7 @@ 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, kbps_limit),
BTRFS_ATTR_PTR(discard, discardable_extents),
BTRFS_ATTR_PTR(discard, discardable_bytes),
NULL,
--
2.17.1