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rhashtable: Supports for nulls marker

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In order to allow for wider usage of rhashtable, use a special nulls
marker to terminate each chain. The reason for not using the existing
nulls_list is that the prev pointer usage would not be valid as entries
can be linked in two different buckets at the same time.

The 4 nulls base bits can be set through the rhashtable_params structure
like this:

struct rhashtable_params params = {
        [...]
        .nulls_base = (1U << RHT_BASE_SHIFT),
};

This reduces the hash length from 32 bits to 27 bits.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Thomas Graf
2015-01-02 23:00:21 +01:00
committed by David S. Miller
parent 97defe1ecf
commit f89bd6f87a
3 changed files with 79 additions and 18 deletions
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57
include/linux/rhashtable.h
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@@ -18,15 +18,32 @@
#ifndef _LINUX_RHASHTABLE_H
#define _LINUX_RHASHTABLE_H
#include <linux/rculist.h>
#include <linux/list_nulls.h>
#include <linux/workqueue.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.
*/
#define RHT_BASE_BITS 4
#define RHT_HASH_BITS 27
#define RHT_BASE_SHIFT RHT_HASH_BITS
struct rhash_head {
struct rhash_head __rcu *next;
};
#define INIT_HASH_HEAD(ptr) ((ptr)->next = NULL)
/**
* struct bucket_table - Table of hash buckets
* @size: Number of hash buckets
@@ -55,6 +72,7 @@ struct rhashtable;
* @hash_rnd: Seed to use while hashing
* @max_shift: Maximum number of shifts while expanding
* @min_shift: Minimum number of shifts while shrinking
* @nulls_base: Base value to generate nulls marker
* @locks_mul: Number of bucket locks to allocate per cpu (default: 128)
* @hashfn: Function to hash key
* @obj_hashfn: Function to hash object
@@ -69,6 +87,7 @@ struct rhashtable_params {
u32 hash_rnd;
size_t max_shift;
size_t min_shift;
u32 nulls_base;
size_t locks_mul;
rht_hashfn_t hashfn;
rht_obj_hashfn_t obj_hashfn;
@@ -100,6 +119,24 @@ struct rhashtable {
bool being_destroyed;
};
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))
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;
}
#ifdef CONFIG_PROVE_LOCKING
int lockdep_rht_mutex_is_held(struct rhashtable *ht);
int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash);
@@ -157,7 +194,7 @@ void rhashtable_destroy(struct rhashtable *ht);
*/
#define rht_for_each_continue(pos, head, tbl, hash) \
for (pos = rht_dereference_bucket(head, tbl, hash); \
pos; \
!rht_is_a_nulls(pos); \
pos = rht_dereference_bucket((pos)->next, tbl, hash))
/**
@@ -180,7 +217,7 @@ void rhashtable_destroy(struct rhashtable *ht);
*/
#define rht_for_each_entry_continue(tpos, pos, head, tbl, hash, member) \
for (pos = rht_dereference_bucket(head, tbl, hash); \
pos && rht_entry(tpos, pos, member); \
(!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
pos = rht_dereference_bucket((pos)->next, tbl, hash))
/**
@@ -209,9 +246,9 @@ void rhashtable_destroy(struct rhashtable *ht);
*/
#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member) \
for (pos = rht_dereference_bucket((tbl)->buckets[hash], tbl, hash), \
next = pos ? rht_dereference_bucket(pos->next, tbl, hash) \
: NULL; \
pos && rht_entry(tpos, pos, member); \
next = !rht_is_a_nulls(pos) ? \
rht_dereference_bucket(pos->next, tbl, hash) : NULL; \
(!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
pos = next)
/**
@@ -228,7 +265,7 @@ void rhashtable_destroy(struct rhashtable *ht);
#define rht_for_each_rcu_continue(pos, head, tbl, hash) \
for (({barrier(); }), \
pos = rht_dereference_bucket_rcu(head, tbl, hash); \
pos; \
!rht_is_a_nulls(pos); \
pos = rcu_dereference_raw(pos->next))
/**
@@ -260,7 +297,7 @@ void rhashtable_destroy(struct rhashtable *ht);
#define rht_for_each_entry_rcu_continue(tpos, pos, head, tbl, hash, member) \
for (({barrier(); }), \
pos = rht_dereference_bucket_rcu(head, tbl, hash); \
pos && rht_entry(tpos, pos, member); \
(!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
pos = rht_dereference_bucket_rcu(pos->next, tbl, hash))
/**