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authorHerbert Xu <herbert@gondor.apana.org.au>2015-03-24 13:37:30 +1100
committerDavid S. Miller <davem@davemloft.net>2015-03-24 14:57:04 -0400
commit27ed44a5d6d88897002b75f53004d4c565a5aab6 (patch)
tree6e1ddb2743ca32a240661bd395160437280d2d03 /lib
parent8263d57e376546bd5da42ea377d22c43239aa317 (diff)
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')
-rw-r--r--lib/rhashtable.c12
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;