[PATCH 03/18] rhashtable: remove nulls_base and related code.

NeilBrown
2018-06-01T04:44:09Z

This "feature" is unused, undocumented, and untested and so
doesn't really belong. Next patch will introduce support
to detect when a search gets diverted down a different chain,
which the common purpose of nulls markers.

This patch actually fixes a bug too. The table resizing allows a
table to grow to 2^31 buckets, but the hash is truncated to 27 bits -
any growth beyond 2^27 is wasteful an ineffective.

This patch results in NULLS_MARKER(0) being used for all chains,
and leaves the use of rht_is_a_null() to test for it.

Signed-off-by: NeilBrown <neilb@suse.com>
---
include/linux/rhashtable-types.h | 2 --
include/linux/rhashtable.h | 33 +++------------------------------
lib/rhashtable.c | 8 --------
lib/test_rhashtable.c | 5 +----
4 files changed, 4 insertions(+), 44 deletions(-)

diff --git a/include/linux/rhashtable-types.h b/include/linux/rhashtable-types.h
index 9740063ff13b..763d613ce2c2 100644
--- a/include/linux/rhashtable-types.h
+++ b/include/linux/rhashtable-types.h
@@ -50,7 +50,6 @@ typedef int (*rht_obj_cmpfn_t)(struct rhashtable_compare_arg *arg,
* @min_size: Minimum size while shrinking
* @locks_mul: Number of bucket locks to allocate per cpu (default: 32)
* @automatic_shrinking: Enable automatic shrinking of tables
- * @nulls_base: Base value to generate nulls marker
* @hashfn: Hash function (default: jhash2 if !(key_len % 4), or jhash)
* @obj_hashfn: Function to hash object
* @obj_cmpfn: Function to compare key with object
@@ -64,7 +63,6 @@ struct rhashtable_params {
u16 min_size;
bool automatic_shrinking;
u8 locks_mul;
- u32 nulls_base;
rht_hashfn_t hashfn;
rht_obj_hashfn_t obj_hashfn;
rht_obj_cmpfn_t obj_cmpfn;
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 48754ab07cdf..d9f719af7936 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -28,25 +28,8 @@
#include <linux/rhashtable-types.h>
/*
* The end of the chain is marked with a special nulls marks which has
- * the following format:
- *
- * +-------+-----------------------------------------------------+-+
- * | Base | Hash |1|
- * +-------+-----------------------------------------------------+-+
- *
- * Base (4 bits) : Reserved to distinguish between multiple tables.
- * Specified via &struct rhashtable_params.nulls_base.
- * Hash (27 bits): Full hash (unmasked) of first element added to bucket
- * 1 (1 bit) : Nulls marker (always set)
- *
- * The remaining bits of the next pointer remain unused for now.
+ * the least significant bit set.
*/
-#define RHT_BASE_BITS 4
-#define RHT_HASH_BITS 27
-#define RHT_BASE_SHIFT RHT_HASH_BITS
-
-/* Base bits plus 1 bit for nulls marker */
-#define RHT_HASH_RESERVED_SPACE (RHT_BASE_BITS + 1)

/* Maximum chain length before rehash
*
@@ -92,24 +75,14 @@ struct bucket_table {
struct rhash_head __rcu *buckets[] ____cacheline_aligned_in_smp;
};

-static inline unsigned long rht_marker(const struct rhashtable *ht, u32 hash)
-{
- return NULLS_MARKER(ht->p.nulls_base + hash);
-}
-
#define INIT_RHT_NULLS_HEAD(ptr, ht, hash) \
- ((ptr) = (typeof(ptr)) rht_marker(ht, hash))
+ ((ptr) = (typeof(ptr)) NULLS_MARKER(0))

static inline bool rht_is_a_nulls(const struct rhash_head *ptr)
{
return ((unsigned long) ptr & 1);
}

-static inline unsigned long rht_get_nulls_value(const struct rhash_head *ptr)
-{
- return ((unsigned long) ptr) >> 1;
-}
-
static inline void *rht_obj(const struct rhashtable *ht,
const struct rhash_head *he)
{
@@ -119,7 +92,7 @@ static inline void *rht_obj(const struct rhashtable *ht,
static inline unsigned int rht_bucket_index(const struct bucket_table *tbl,
unsigned int hash)
{
- return (hash >> RHT_HASH_RESERVED_SPACE) & (tbl->size - 1);
+ return hash & (tbl->size - 1);
}

static inline unsigned int rht_key_get_hash(struct rhashtable *ht,
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index c9fafea7dc6e..688693c919be 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -995,7 +995,6 @@ static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
* .key_offset = offsetof(struct test_obj, key),
* .key_len = sizeof(int),
* .hashfn = jhash,
- * .nulls_base = (1U << RHT_BASE_SHIFT),
* };
*
* Configuration Example 2: Variable length keys
@@ -1029,9 +1028,6 @@ int rhashtable_init(struct rhashtable *ht,
(params->obj_hashfn && !params->obj_cmpfn))
return -EINVAL;

- if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
- return -EINVAL;
-
memset(ht, 0, sizeof(*ht));
mutex_init(&ht->mutex);
spin_lock_init(&ht->lock);
@@ -1096,10 +1092,6 @@ int rhltable_init(struct rhltable *hlt, const struct rhashtable_params *params)
{
int err;

- /* No rhlist NULLs marking for now. */
- if (params->nulls_base)
- return -EINVAL;
-
err = rhashtable_init(&hlt->ht, params);
hlt->ht.rhlist = true;
return err;
diff --git a/lib/test_rhashtable.c b/lib/test_rhashtable.c
index bf92b7aa2a49..b428a9c7522a 100644
--- a/lib/test_rhashtable.c
+++ b/lib/test_rhashtable.c
@@ -83,7 +83,7 @@ static u32 my_hashfn(const void *data, u32 len, u32 seed)
{
const struct test_obj_rhl *obj = data;

- return (obj->value.id % 10) << RHT_HASH_RESERVED_SPACE;
+ return (obj->value.id % 10);
}

static int my_cmpfn(struct rhashtable_compare_arg *arg, const void *obj)
@@ -99,7 +99,6 @@ static struct rhashtable_params test_rht_params = {
.key_offset = offsetof(struct test_obj, value),
.key_len = sizeof(struct test_obj_val),
.hashfn = jhash,
- .nulls_base = (3U << RHT_BASE_SHIFT),
};

static struct rhashtable_params test_rht_params_dup = {
@@ -294,8 +293,6 @@ static int __init test_rhltable(unsigned int entries)
if (!obj_in_table)
goto out_free;

- /* nulls_base not supported in rhlist interface */
- test_rht_params.nulls_base = 0;
err = rhltable_init(&rhlt, &test_rht_params);
if (WARN_ON(err))
goto out_free;