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rhashtable: Add comment on choice of elasticity value 

This patch adds a comment on the choice of the value 16 as the
maximum chain length before we force a rehash.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Herbert Xu 2015-03-24 13:37:30 +11:00 committed by David S. Miller
parent 8263d57e37
commit 27ed44a5d6
1 changed files with 12 additions and 0 deletions
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12
lib/rhashtable.c
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@ -736,6 +736,18 @@ int rhashtable_init(struct rhashtable *ht,
ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
/* The maximum (not average) chain length grows with the
* size of the hash table, at a rate of (log N)/(log log N).
* The value of 16 is selected so that even if the hash
* table grew to 2^32 you would not expect the maximum
* chain length to exceed it unless we are under attack
* (or extremely unlucky).
*
* As this limit is only to detect attacks, we don't need
* to set it to a lower value as you'd need the chain
* length to vastly exceed 16 to have any real effect
* on the system.
*/
if (!params->insecure_elasticity)
ht->elasticity = 16;