From: Zqiang <[email protected]> Add free per-cpu existing krcp's page cache operation, when the system is under memory pressure.
Signed-off-by: Zqiang <[email protected]> Co-developed-by: Uladzislau Rezki (Sony) <[email protected]> --- v1->v2->v3->v4: During the test a page shrinker is pretty active, because of low memory condition. callback drains it whereas kvfree_rcu() part refill it right away making kind of vicious circle. Through Vlad Rezki suggestion, to avoid this, schedule a periodic delayed work with HZ, and it's easy to do that. kernel/rcu/tree.c | 50 +++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 8 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c1ae1e52f638..f3b772eef468 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3139,7 +3139,7 @@ struct kfree_rcu_cpu { bool initialized; int count; - struct work_struct page_cache_work; + struct delayed_work page_cache_work; atomic_t work_in_progress; struct hrtimer hrtimer; @@ -3395,7 +3395,7 @@ schedule_page_work_fn(struct hrtimer *t) struct kfree_rcu_cpu *krcp = container_of(t, struct kfree_rcu_cpu, hrtimer); - queue_work(system_highpri_wq, &krcp->page_cache_work); + queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0); return HRTIMER_NORESTART; } @@ -3404,7 +3404,7 @@ static void fill_page_cache_func(struct work_struct *work) struct kvfree_rcu_bulk_data *bnode; struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, - page_cache_work); + page_cache_work.work); unsigned long flags; bool pushed; int i; @@ -3428,15 +3428,22 @@ static void fill_page_cache_func(struct work_struct *work) atomic_set(&krcp->work_in_progress, 0); } +static bool backoff_page_cache_fill; + static void run_page_cache_worker(struct kfree_rcu_cpu *krcp) { if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && !atomic_xchg(&krcp->work_in_progress, 1)) { - hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, - HRTIMER_MODE_REL); - krcp->hrtimer.function = schedule_page_work_fn; - hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + if (READ_ONCE(backoff_page_cache_fill)) { + queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, HZ); + WRITE_ONCE(backoff_page_cache_fill, false); + } else { + hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, + HRTIMER_MODE_REL); + krcp->hrtimer.function = schedule_page_work_fn; + hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + } } } @@ -3571,19 +3578,44 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) } EXPORT_SYMBOL_GPL(kvfree_call_rcu); +static int free_krc_page_cache(struct kfree_rcu_cpu *krcp) +{ + unsigned long flags; + struct llist_node *page_list, *pos, *n; + int freed = 0; + + raw_spin_lock_irqsave(&krcp->lock, flags); + page_list = llist_del_all(&krcp->bkvcache); + krcp->nr_bkv_objs = 0; + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + llist_for_each_safe(pos, n, page_list) { + free_page((unsigned long)pos); + freed++; + } + + return freed; +} + static unsigned long kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { int cpu; unsigned long count = 0; + unsigned long flags; /* Snapshot count of all CPUs */ for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); count += READ_ONCE(krcp->count); + + raw_spin_lock_irqsave(&krcp->lock, flags); + count += krcp->nr_bkv_objs; + raw_spin_unlock_irqrestore(&krcp->lock, flags); } + WRITE_ONCE(backoff_page_cache_fill, true); return count; } @@ -3598,6 +3630,8 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); count = krcp->count; + count += free_krc_page_cache(krcp); + raw_spin_lock_irqsave(&krcp->lock, flags); if (krcp->monitor_todo) kfree_rcu_drain_unlock(krcp, flags); @@ -4574,7 +4608,7 @@ static void __init kfree_rcu_batch_init(void) } INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor); - INIT_WORK(&krcp->page_cache_work, fill_page_cache_func); + INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func); krcp->initialized = true; } if (register_shrinker(&kfree_rcu_shrinker)) -- 2.17.1
