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author | Herbert Xu <herbert@gondor.apana.org.au> | 2015-03-24 13:37:30 +1100 |
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committer | David S. Miller <davem@davemloft.net> | 2015-03-24 14:57:04 -0400 |
commit | 27ed44a5d6d88897002b75f53004d4c565a5aab6 (patch) | |
tree | 6e1ddb2743ca32a240661bd395160437280d2d03 /lib/rhashtable.c | |
parent | 8263d57e376546bd5da42ea377d22c43239aa317 (diff) | |
download | linux-27ed44a5d6d88897002b75f53004d4c565a5aab6.tar.bz2 |
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>
Diffstat (limited to 'lib/rhashtable.c')
-rw-r--r-- | lib/rhashtable.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/lib/rhashtable.c b/lib/rhashtable.c index e96ad1a52c90..8514f7c5f029 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -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; |