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Message-ID: <20210212154503.GA55693@pc638.lan>
Date: Fri, 12 Feb 2021 16:45:03 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: qiang.zhang@...driver.com
Cc: urezki@...il.com, paulmck@...nel.org, joel@...lfernandes.org,
rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] kvfree_rcu: Release page cache under memory pressure
> From: Zqiang <qiang.zhang@...driver.com>
>
> Add free per-cpu existing krcp's page cache operation in shrink callback
> function, and also during shrink period, simple delay schedule fill page
> work, to avoid refill page while free krcp page cache.
>
> Signed-off-by: Zqiang <qiang.zhang@...driver.com>
> Co-developed-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
> v1->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.
> v4->v5:
> change commit message and use xchg replace WRITE_ONCE()
>
> kernel/rcu/tree.c | 49 +++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 41 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index c1ae1e52f638..f1fba23f5036 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 +3428,21 @@ static void fill_page_cache_func(struct work_struct *work)
> atomic_set(&krcp->work_in_progress, 0);
> }
>
> +static atomic_t backoff_page_cache_fill = ATOMIC_INIT(0);
> +
Should we initialize a static atomic_t? It is zero by default.
> 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 (atomic_xchg(&backoff_page_cache_fill, 0)) {
> + queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, HZ);
system_wq? It is not so critical, anyway the job is rearmed with 1 second interval.
> + } 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 +3577,44 @@ 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);
> }
>
> + atomic_set(&backoff_page_cache_fill, 1);
> return count;
> }
>
> @@ -3598,6 +3629,8 @@ 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 +4607,7 @@ 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))
> --
> 2.25.1
>
I have reviewed and tested that patch. Even though it can not be applied
cleanly on the latest Paul "dev" branch feel free to use:
Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>
Tested-by: Uladzislau Rezki (Sony) <urezki@...il.com>
Also i placed some small nits, because it should be rebased on latest dev.
As for commit message i guess Paul will help :)
Thank you!
--
Vlad Rezki
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