From cd0893369ca85fd11bc517081b2d9079d2ef2f90 Mon Sep 17 00:00:00 2001 From: "David S. Miller" Date: Mon, 11 Jul 2011 01:28:12 -0700 Subject: [PATCH] neigh: Store hash shift instead of mask. And mask the hash function result by simply shifting down the "->hash_shift" most significant bits. Currently which bits we use is arbitrary since jhash produces entropy evenly across the whole hash function result. But soon we'll be using universal hashing functions, and in those cases more entropy exists in the higher bits than the lower bits, because they use multiplies. Signed-off-by: David S. Miller --- include/net/neighbour.h | 2 +- net/core/neighbour.c | 47 ++++++++++++++++++++--------------------- 2 files changed, 24 insertions(+), 25 deletions(-) diff --git a/include/net/neighbour.h b/include/net/neighbour.h index 4014b623880c..6fe8c2cd5acb 100644 --- a/include/net/neighbour.h +++ b/include/net/neighbour.h @@ -142,7 +142,7 @@ struct pneigh_entry { struct neigh_hash_table { struct neighbour __rcu **hash_buckets; - unsigned int hash_mask; + unsigned int hash_shift; __u32 hash_rnd; struct rcu_head rcu; }; diff --git a/net/core/neighbour.c b/net/core/neighbour.c index ceb505b1507c..4d5fc9433fd9 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -137,7 +137,7 @@ static int neigh_forced_gc(struct neigh_table *tbl) write_lock_bh(&tbl->lock); nht = rcu_dereference_protected(tbl->nht, lockdep_is_held(&tbl->lock)); - for (i = 0; i <= nht->hash_mask; i++) { + for (i = 0; i < (1 << nht->hash_shift); i++) { struct neighbour *n; struct neighbour __rcu **np; @@ -210,7 +210,7 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev) nht = rcu_dereference_protected(tbl->nht, lockdep_is_held(&tbl->lock)); - for (i = 0; i <= nht->hash_mask; i++) { + for (i = 0; i < (1 << nht->hash_shift); i++) { struct neighbour *n; struct neighbour __rcu **np = &nht->hash_buckets[i]; @@ -312,9 +312,9 @@ out_entries: goto out; } -static struct neigh_hash_table *neigh_hash_alloc(unsigned int entries) +static struct neigh_hash_table *neigh_hash_alloc(unsigned int shift) { - size_t size = entries * sizeof(struct neighbour *); + size_t size = (1 << shift) * sizeof(struct neighbour *); struct neigh_hash_table *ret; struct neighbour __rcu **buckets; @@ -332,7 +332,7 @@ static struct neigh_hash_table *neigh_hash_alloc(unsigned int entries) return NULL; } ret->hash_buckets = buckets; - ret->hash_mask = entries - 1; + ret->hash_shift = shift; get_random_bytes(&ret->hash_rnd, sizeof(ret->hash_rnd)); return ret; } @@ -342,7 +342,7 @@ static void neigh_hash_free_rcu(struct rcu_head *head) struct neigh_hash_table *nht = container_of(head, struct neigh_hash_table, rcu); - size_t size = (nht->hash_mask + 1) * sizeof(struct neighbour *); + size_t size = (1 << nht->hash_shift) * sizeof(struct neighbour *); struct neighbour __rcu **buckets = nht->hash_buckets; if (size <= PAGE_SIZE) @@ -353,21 +353,20 @@ static void neigh_hash_free_rcu(struct rcu_head *head) } static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl, - unsigned long new_entries) + unsigned long new_shift) { unsigned int i, hash; struct neigh_hash_table *new_nht, *old_nht; NEIGH_CACHE_STAT_INC(tbl, hash_grows); - BUG_ON(!is_power_of_2(new_entries)); old_nht = rcu_dereference_protected(tbl->nht, lockdep_is_held(&tbl->lock)); - new_nht = neigh_hash_alloc(new_entries); + new_nht = neigh_hash_alloc(new_shift); if (!new_nht) return old_nht; - for (i = 0; i <= old_nht->hash_mask; i++) { + for (i = 0; i < (1 << old_nht->hash_shift); i++) { struct neighbour *n, *next; for (n = rcu_dereference_protected(old_nht->hash_buckets[i], @@ -377,7 +376,7 @@ static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl, hash = tbl->hash(n->primary_key, n->dev, new_nht->hash_rnd); - hash &= new_nht->hash_mask; + hash >>= (32 - new_nht->hash_shift); next = rcu_dereference_protected(n->next, lockdep_is_held(&tbl->lock)); @@ -406,7 +405,7 @@ struct neighbour *neigh_lookup(struct neigh_table *tbl, const void *pkey, rcu_read_lock_bh(); nht = rcu_dereference_bh(tbl->nht); - hash_val = tbl->hash(pkey, dev, nht->hash_rnd) & nht->hash_mask; + hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift); for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]); n != NULL; @@ -436,7 +435,7 @@ struct neighbour *neigh_lookup_nodev(struct neigh_table *tbl, struct net *net, rcu_read_lock_bh(); nht = rcu_dereference_bh(tbl->nht); - hash_val = tbl->hash(pkey, NULL, nht->hash_rnd) & nht->hash_mask; + hash_val = tbl->hash(pkey, NULL, nht->hash_rnd) >> (32 - nht->hash_shift); for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]); n != NULL; @@ -492,10 +491,10 @@ struct neighbour *neigh_create(struct neigh_table *tbl, const void *pkey, nht = rcu_dereference_protected(tbl->nht, lockdep_is_held(&tbl->lock)); - if (atomic_read(&tbl->entries) > (nht->hash_mask + 1)) - nht = neigh_hash_grow(tbl, (nht->hash_mask + 1) << 1); + if (atomic_read(&tbl->entries) > (1 << nht->hash_shift)) + nht = neigh_hash_grow(tbl, nht->hash_shift + 1); - hash_val = tbl->hash(pkey, dev, nht->hash_rnd) & nht->hash_mask; + hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift); if (n->parms->dead) { rc = ERR_PTR(-EINVAL); @@ -784,7 +783,7 @@ static void neigh_periodic_work(struct work_struct *work) neigh_rand_reach_time(p->base_reachable_time); } - for (i = 0 ; i <= nht->hash_mask; i++) { + for (i = 0 ; i < (1 << nht->hash_shift); i++) { np = &nht->hash_buckets[i]; while ((n = rcu_dereference_protected(*np, @@ -1540,7 +1539,7 @@ void neigh_table_init_no_netlink(struct neigh_table *tbl) panic("cannot create neighbour proc dir entry"); #endif - RCU_INIT_POINTER(tbl->nht, neigh_hash_alloc(8)); + RCU_INIT_POINTER(tbl->nht, neigh_hash_alloc(3)); phsize = (PNEIGH_HASHMASK + 1) * sizeof(struct pneigh_entry *); tbl->phash_buckets = kzalloc(phsize, GFP_KERNEL); @@ -1857,7 +1856,7 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl, rcu_read_lock_bh(); nht = rcu_dereference_bh(tbl->nht); ndc.ndtc_hash_rnd = nht->hash_rnd; - ndc.ndtc_hash_mask = nht->hash_mask; + ndc.ndtc_hash_mask = ((1 << nht->hash_shift) - 1); rcu_read_unlock_bh(); NLA_PUT(skb, NDTA_CONFIG, sizeof(ndc), &ndc); @@ -2200,7 +2199,7 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb, rcu_read_lock_bh(); nht = rcu_dereference_bh(tbl->nht); - for (h = 0; h <= nht->hash_mask; h++) { + for (h = 0; h < (1 << nht->hash_shift); h++) { if (h < s_h) continue; if (h > s_h) @@ -2264,7 +2263,7 @@ void neigh_for_each(struct neigh_table *tbl, void (*cb)(struct neighbour *, void nht = rcu_dereference_bh(tbl->nht); read_lock(&tbl->lock); /* avoid resizes */ - for (chain = 0; chain <= nht->hash_mask; chain++) { + for (chain = 0; chain < (1 << nht->hash_shift); chain++) { struct neighbour *n; for (n = rcu_dereference_bh(nht->hash_buckets[chain]); @@ -2286,7 +2285,7 @@ void __neigh_for_each_release(struct neigh_table *tbl, nht = rcu_dereference_protected(tbl->nht, lockdep_is_held(&tbl->lock)); - for (chain = 0; chain <= nht->hash_mask; chain++) { + for (chain = 0; chain < (1 << nht->hash_shift); chain++) { struct neighbour *n; struct neighbour __rcu **np; @@ -2323,7 +2322,7 @@ static struct neighbour *neigh_get_first(struct seq_file *seq) int bucket = state->bucket; state->flags &= ~NEIGH_SEQ_IS_PNEIGH; - for (bucket = 0; bucket <= nht->hash_mask; bucket++) { + for (bucket = 0; bucket < (1 << nht->hash_shift); bucket++) { n = rcu_dereference_bh(nht->hash_buckets[bucket]); while (n) { @@ -2390,7 +2389,7 @@ next: if (n) break; - if (++state->bucket > nht->hash_mask) + if (++state->bucket >= (1 << nht->hash_shift)) break; n = rcu_dereference_bh(nht->hash_buckets[state->bucket]); -- 2.34.1