linux-kernel - Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

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Date:	Fri, 03 Aug 2012 19:39:10 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, paul.gortmaker@...driver.com,
	davem@...emloft.net, rostedt@...dmis.org, mingo@...e.hu,
	ebiederm@...ssion.com, aarcange@...hat.com, ericvh@...il.com,
	netdev@...r.kernel.org
Subject: Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

On Fri, 2012-08-03 at 16:23 +0200, Sasha Levin wrote:
> This hashtable implementation is using hlist buckets to provide a simple
> hashtable to prevent it from getting reimplemented all over the kernel.
> 

> +static void hash_add(struct hash_table *ht, struct hlist_node *node, long key)
> +{
> +	hlist_add_head(node,
> +		&ht->buckets[hash_long((unsigned long)key, HASH_BITS(ht))]);
> +}
> +

Why key is a long, casted later to "unsigned long" ?

hash_long() is expensive on 64bit arches, and not really needed
if key is an u32 from the beginning ( I am referring to your patches 6 &
7 using jhash()  )

Maybe you could use a macro, so that we can automatically select
hash_32() if key is an u32, and hash_long() for other types.



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