From c542ee149230c4c3fc086feae608230e7aa97fcf Mon Sep 17 00:00:00 2001 From: Benjamin Marzinski Date: Tue, 7 May 2024 17:16:24 -0400 Subject: dm-delay: change locking to avoid contention The delayed_bios list is protected by one mutex shared by all dm-delay devices. This mutex must be held whenever a bio is added or expired bios are removed from the list. Since a large number of expired bios could be on the list, flush_delayed_bios() can schedule while holding the mutex. This means a flush_delayed_bios() call on any dm-delay device can slow down delay_map() calls on any other dm-delay device. To keep dm-delay devices from slowing each other down and keep processing delay bios from slowing adding delayed bios, the global mutex has been removed, and each dm-delay device now has two locks. delayed_bios_lock is a spinlock that must be held whenever the delayed_bios list is accessed. process_bios_lock is a mutex that must be held whenever a process has temporarily pulled bios off the delayed_bios list to check which ones should be processed. It must be held until all the bios that won't be processed are returned to the list. This is what flush_delayed_bios() now does. The mutex is necessary to guarantee that delay_presuspend() sees the entire list of delayed bios when it calls flush_delayed_bios(). Signed-off-by: Benjamin Marzinski Signed-off-by: Mike Snitzer --- drivers/md/dm-delay.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-) (limited to 'drivers/md') diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c index 2ac43d1f1b92..da3f8131d52c 100644 --- a/drivers/md/dm-delay.c +++ b/drivers/md/dm-delay.c @@ -29,6 +29,8 @@ struct delay_class { struct delay_c { struct timer_list delay_timer; struct mutex timer_lock; + struct mutex process_bios_lock; /* hold while removing bios to be processed from list */ + spinlock_t delayed_bios_lock; /* hold on all accesses to delayed_bios list */ struct workqueue_struct *kdelayd_wq; struct work_struct flush_expired_bios; struct list_head delayed_bios; @@ -49,8 +51,6 @@ struct dm_delay_info { unsigned long expires; }; -static DEFINE_MUTEX(delayed_bios_lock); - static void handle_delayed_timer(struct timer_list *t) { struct delay_c *dc = from_timer(dc, t, delay_timer); @@ -89,12 +89,16 @@ static void flush_delayed_bios(struct delay_c *dc, bool flush_all) { struct dm_delay_info *delayed, *next; struct bio_list flush_bio_list; + LIST_HEAD(local_list); unsigned long next_expires = 0; bool start_timer = false; bio_list_init(&flush_bio_list); - mutex_lock(&delayed_bios_lock); - list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) { + mutex_lock(&dc->process_bios_lock); + spin_lock(&dc->delayed_bios_lock); + list_replace_init(&dc->delayed_bios, &local_list); + spin_unlock(&dc->delayed_bios_lock); + list_for_each_entry_safe(delayed, next, &local_list, list) { cond_resched(); if (flush_all || time_after_eq(jiffies, delayed->expires)) { struct bio *bio = dm_bio_from_per_bio_data(delayed, @@ -114,7 +118,10 @@ static void flush_delayed_bios(struct delay_c *dc, bool flush_all) } } } - mutex_unlock(&delayed_bios_lock); + spin_lock(&dc->delayed_bios_lock); + list_splice(&local_list, &dc->delayed_bios); + spin_unlock(&dc->delayed_bios_lock); + mutex_unlock(&dc->process_bios_lock); if (start_timer) queue_timeout(dc, next_expires); @@ -128,13 +135,13 @@ static int flush_worker_fn(void *data) while (!kthread_should_stop()) { flush_delayed_bios(dc, false); - mutex_lock(&delayed_bios_lock); + spin_lock(&dc->delayed_bios_lock); if (unlikely(list_empty(&dc->delayed_bios))) { set_current_state(TASK_INTERRUPTIBLE); - mutex_unlock(&delayed_bios_lock); + spin_unlock(&dc->delayed_bios_lock); schedule(); } else { - mutex_unlock(&delayed_bios_lock); + spin_unlock(&dc->delayed_bios_lock); cond_resched(); } } @@ -168,6 +175,7 @@ static void delay_dtr(struct dm_target *ti) if (dc->worker) kthread_stop(dc->worker); + mutex_destroy(&dc->process_bios_lock); mutex_destroy(&dc->timer_lock); kfree(dc); @@ -227,6 +235,8 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) ti->private = dc; INIT_LIST_HEAD(&dc->delayed_bios); mutex_init(&dc->timer_lock); + mutex_init(&dc->process_bios_lock); + spin_lock_init(&dc->delayed_bios_lock); dc->may_delay = true; dc->argc = argc; @@ -309,14 +319,14 @@ static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio) delayed->context = dc; delayed->expires = expires = jiffies + msecs_to_jiffies(c->delay); - mutex_lock(&delayed_bios_lock); + spin_lock(&dc->delayed_bios_lock); if (unlikely(!dc->may_delay)) { - mutex_unlock(&delayed_bios_lock); + spin_unlock(&dc->delayed_bios_lock); return DM_MAPIO_REMAPPED; } c->ops++; list_add_tail(&delayed->list, &dc->delayed_bios); - mutex_unlock(&delayed_bios_lock); + spin_unlock(&dc->delayed_bios_lock); if (delay_is_fast(dc)) wake_up_process(dc->worker); @@ -330,9 +340,9 @@ static void delay_presuspend(struct dm_target *ti) { struct delay_c *dc = ti->private; - mutex_lock(&delayed_bios_lock); + spin_lock(&dc->delayed_bios_lock); dc->may_delay = false; - mutex_unlock(&delayed_bios_lock); + spin_unlock(&dc->delayed_bios_lock); if (!delay_is_fast(dc)) timer_delete(&dc->delay_timer); -- cgit v1.2.3