linux-kernel - Re: [PATCH] kvfree_rcu: Release page cache under memory pressure

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Date:   Thu, 28 Jan 2021 17:31:49 +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] kvfree_rcu: Release page cache under memory pressure

Hello, Zqiang.

See below some nits:

> 
> Add free per-cpu existing krcp's page cache operation, when
> the system is under memory pressure.
> 
> Signed-off-by: Zqiang <qiang.zhang@...driver.com>
> ---
>  kernel/rcu/tree.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index c1ae1e52f638..4e1c14b12bdd 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3571,17 +3571,41 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
>  }
>  EXPORT_SYMBOL_GPL(kvfree_call_rcu);
>  
> +static inline int free_krc_page_cache(struct kfree_rcu_cpu *krcp)
Do we need it "inlined"?

> +{
> +	unsigned long flags;
> +	struct kvfree_rcu_bulk_data *bnode;
> +	int i, num = 0;
> +
> +	for (i = 0; i < rcu_min_cached_objs; i++) {
> +		raw_spin_lock_irqsave(&krcp->lock, flags);
> +		bnode = get_cached_bnode(krcp);
> +		raw_spin_unlock_irqrestore(&krcp->lock, flags);
> +		if (!bnode)
> +			break;
> +		free_page((unsigned long)bnode);
> +		num++;
> +	}
> +
> +	return num;
Get rid of "num" and return i instead?

> +}
> +
>  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);
>  	}
>  
>  	return count;
> @@ -3604,6 +3628,8 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
>  		else
>  			raw_spin_unlock_irqrestore(&krcp->lock, flags);
>  
> +		count += free_krc_page_cache(krcp);
Move it upper right after count = krcp->count;, so a "count" is set
in one place what i more readable and clear?

Thank you!

--
Vlad Rezki