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Commit 9f9a7077 authored by NeilBrown's avatar NeilBrown Committed by David S. Miller
Browse files

rhashtable: remove nulls_base and related code. 



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: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0eb71a9d

include/linux/rhashtable-types.h

+0 −2
Original line number Diff line number Diff line
@@ -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;

include/linux/rhashtable.h

+3 −30
Original line number Diff line number Diff line
@@ -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,

lib/rhashtable.c

+0 −8
Original line number Diff line number Diff line
@@ -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;

lib/test_rhashtable.c

+1 −4
Original line number Diff line number Diff line
@@ -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;

net/core/xdp.c

+2 −2
Original line number Diff line number Diff line
@@ -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,