netdev - RE: [v1 PATCH 1/14] rhashtable: Remove shift from bucket

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Date:	Tue, 17 Mar 2015 10:51:25 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Herbert Xu' <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	"tgraf@...g.ch" <tgraf@...g.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: RE: [v1 PATCH 1/14] rhashtable: Remove shift from bucket_table

From: Herbert Xu
> Sent: 15 March 2015 10:44
> Keeping both size and shift is silly.  We only need one.
...
> --- a/lib/rhashtable.c
> +++ b/lib/rhashtable.c
> @@ -162,7 +162,6 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
>  		return NULL;
> 
>  	tbl->size = nbuckets;
> -	tbl->shift = ilog2(nbuckets);
> 
>  	if (alloc_bucket_locks(ht, tbl) < 0) {
>  		bucket_table_free(tbl);
> @@ -189,7 +188,7 @@ static bool rht_grow_above_75(const struct rhashtable *ht,
>  {
>  	/* Expand table when exceeding 75% load */
>  	return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
> -	       (!ht->p.max_shift || tbl->shift < ht->p.max_shift);
> +	       (!ht->p.max_shift || tbl->size < (1 << ht->p.max_shift));

Looks like you could pre-calculate the 'grow_at' size.
The test above would then be:
	return atomic_read(&ht->nelems > tbl->grow_at_size);

Similarly for the shrink.

	David

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