linux-kernel - Re: [PATCH 5/5] rhashtable: Per bucket locks & expansion/shrinking in work queue

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Date:	Mon, 15 Sep 2014 08:23:00 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	davem@...emloft.net, paulmck@...ux.vnet.ibm.com,
	john.r.fastabend@...el.com, kaber@...sh.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] rhashtable: Per bucket locks & expansion/shrinking
 in work queue

On Mon, 2014-09-15 at 14:18 +0200, Thomas Graf wrote:

> +static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl)
> +{
> +	unsigned int i, size;
> +#if defined(CONFIG_PROVE_LOCKING)
> +	unsigned int nr_pcpus = 2;
> +#else
> +	unsigned int nr_pcpus = num_possible_cpus();
> +#endif
> +
> +	nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
> +	size = nr_pcpus * ht->p.locks_mul;
> +

You need to roundup to next power of two.

> +	if (sizeof(spinlock_t) != 0) {
> +#ifdef CONFIG_NUMA
> +		if (size * sizeof(spinlock_t) > PAGE_SIZE)
> +			tbl->locks = vmalloc(size * sizeof(spinlock_t));
> +		else
> +#endif
> +		tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
> +					   GFP_KERNEL);
> +		if (!tbl->locks)
> +			return -ENOMEM;
> +		for (i = 0; i < size; i++)
> +			spin_lock_init(&tbl->locks[i]);
> +	}
> +	tbl->locks_mask = size - 1;
> +
> +	return 0;
> +}


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