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Message-Id: <E1YWMLD-0000CV-VK@gondolin.me.apana.org.au>
Date: Fri, 13 Mar 2015 20:57:15 +1100
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org
Subject: [PATCH 6/6] rhashtable: Move future_tbl into struct bucket_table
This patch moves future_tbl to open up the possibility of having
multiple rehashes on the same table.
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
---
include/linux/rhashtable.h | 5 +++--
lib/rhashtable.c | 27 +++++++++++----------------
2 files changed, 14 insertions(+), 18 deletions(-)
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index ed7562a..1695378 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -56,6 +56,7 @@ struct rhash_head {
* @locks: Array of spinlocks protecting individual buckets
* @walkers: List of active walkers
* @rcu: RCU structure for freeing the table
+ * @future_tbl: Table under construction during rehashing
* @buckets: size * hash buckets
*/
struct bucket_table {
@@ -68,6 +69,8 @@ struct bucket_table {
struct list_head walkers;
struct rcu_head rcu;
+ struct bucket_table __rcu *future_tbl;
+
struct rhash_head __rcu *buckets[] ____cacheline_aligned_in_smp;
};
@@ -105,7 +108,6 @@ struct rhashtable_params {
/**
* struct rhashtable - Hash table handle
* @tbl: Bucket table
- * @future_tbl: Table under construction during expansion/shrinking
* @nelems: Number of elements in table
* @p: Configuration parameters
* @run_work: Deferred worker to expand/shrink asynchronously
@@ -114,7 +116,6 @@ struct rhashtable_params {
*/
struct rhashtable {
struct bucket_table __rcu *tbl;
- struct bucket_table __rcu *future_tbl;
atomic_t nelems;
bool being_destroyed;
struct rhashtable_params p;
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index ff4ea17..9d53a46 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -207,8 +207,9 @@ static bool rht_shrink_below_30(const struct rhashtable *ht,
static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
{
- struct bucket_table *new_tbl = rht_dereference(ht->future_tbl, ht);
struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
+ struct bucket_table *new_tbl =
+ rht_dereference(old_tbl->future_tbl, ht) ?: old_tbl;
struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
int err = -ENOENT;
struct rhash_head *head, *next, *entry;
@@ -273,10 +274,8 @@ static void rhashtable_rehash(struct rhashtable *ht,
/* Make insertions go into the new, empty table right away. Deletions
* and lookups will be attempted in both tables until we synchronize.
- * The synchronize_rcu() guarantees for the new table to be picked up
- * so no new additions go into the old table while we relink.
*/
- rcu_assign_pointer(ht->future_tbl, new_tbl);
+ rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
/* Ensure the new table is visible to readers. */
smp_wmb();
@@ -400,7 +399,7 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
* also grab the bucket lock in old_tbl because until the
* rehash completes ht->tbl won't be changed.
*/
- tbl = rht_dereference_rcu(ht->future_tbl, ht);
+ tbl = rht_dereference_rcu(old_tbl->future_tbl, ht) ?: old_tbl;
if (tbl != old_tbl) {
hash = head_hashfn(ht, tbl, obj);
spin_lock_nested(bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
@@ -525,7 +524,7 @@ bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
* visible then that guarantees the entry to still be in
* old_tbl if it exists.
*/
- tbl = rht_dereference_rcu(ht->future_tbl, ht);
+ tbl = rht_dereference_rcu(old_tbl->future_tbl, ht) ?: old_tbl;
if (!ret && old_tbl != tbl)
ret = __rhashtable_remove(ht, tbl, obj);
@@ -599,7 +598,7 @@ EXPORT_SYMBOL_GPL(rhashtable_lookup);
void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
bool (*compare)(void *, void *), void *arg)
{
- const struct bucket_table *tbl, *old_tbl;
+ const struct bucket_table *tbl;
struct rhash_head *he;
u32 hash;
@@ -618,9 +617,8 @@ restart:
/* Ensure we see any new tables. */
smp_rmb();
- old_tbl = tbl;
- tbl = rht_dereference_rcu(ht->future_tbl, ht);
- if (unlikely(tbl != old_tbl))
+ tbl = rht_dereference_rcu(tbl->future_tbl, ht);
+ if (unlikely(tbl))
goto restart;
rcu_read_unlock();
@@ -830,14 +828,13 @@ next:
iter->skip = 0;
}
- iter->walker->tbl = rht_dereference_rcu(ht->future_tbl, ht);
- if (iter->walker->tbl != tbl) {
+ iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht);
+ if (iter->walker->tbl) {
iter->slot = 0;
iter->skip = 0;
return ERR_PTR(-EAGAIN);
}
- iter->walker->tbl = NULL;
iter->p = NULL;
out:
@@ -865,8 +862,7 @@ void rhashtable_walk_stop(struct rhashtable_iter *iter)
ht = iter->ht;
mutex_lock(&ht->mutex);
- if (rht_dereference(ht->tbl, ht) == tbl ||
- rht_dereference(ht->future_tbl, ht) == tbl)
+ if (tbl->rehash < tbl->size)
list_add(&iter->walker->list, &tbl->walkers);
else
iter->walker->tbl = NULL;
@@ -961,7 +957,6 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
atomic_set(&ht->nelems, 0);
RCU_INIT_POINTER(ht->tbl, tbl);
- RCU_INIT_POINTER(ht->future_tbl, tbl);
INIT_WORK(&ht->run_work, rht_deferred_worker);
--
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