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rhashtable: remove nulls_base and related code.

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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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33
include/linux/rhashtable.h
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@@ -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,