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@xxxxxxxxxx>
> > Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > ---
> > 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
