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rhashtable: remove nulls_base and related code.

Browse source 
This "feature" is unused, undocumented, and untested and so doesn't
really belong.  A patch is under development to properly implement
support for detecting 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.

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
NeilBrown 2018-06-18 12:52:50 +10:00 • committed by David S. Miller
parent 0eb71a9da5
commit 9f9a707738
5 changed files with 6 additions and 46 deletions
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2
include/linux/rhashtable-types.h
View file

@ -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;

33
include/linux/rhashtable.h
View file

@ -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,

8
lib/rhashtable.c
View file

@ -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;

5
lib/test_rhashtable.c
View file

@ -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 = {
@ -296,8 +295,6 @@ 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;

4
net/core/xdp.c
View file

@ -45,8 +45,8 @@ static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
BUILD_BUG_ON(FIELD_SIZEOF(struct xdp_mem_allocator, mem.id)
!= sizeof(u32));
/* Use cyclic increasing ID as direct hash key, see rht_bucket_index */
return key << RHT_HASH_RESERVED_SPACE;
/* Use cyclic increasing ID as direct hash key */
return key;
}
static int xdp_mem_id_cmp(struct rhashtable_compare_arg *arg,