[PATCH 8/9] lib: Closed hash table with low overhead

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Am 26.08.2017 um 09:19 schrieb Felix Kuehling:
> This adds a closed hash table implementation with low memory and CPU
> overhead. The API is inspired by kfifo.
>
> Storing, retrieving and deleting data does not involve any dynamic
> memory management, which makes it ideal for use in interrupt context.
> Memory overhead per entry is the 32 or 64 bit hash key, two bits for
> free/used tracking and whatever value size is stored in the table.
> No list heads or pointers, therefore this data structure should be
> quite cache-friendly, too.
>
> After entries are removed, free space maintenance is necessary. At
> the same time, entries that had hash collisions on insertion can be
> relocated to speed up future lookups. This is done incrementally and
> opportunistically to avoid long stalls.
>
> CPU overhead is very small as long as the table doesn't fill up more
> than about 50%. It's still quite efficient up to 90% full. The less
> free space is in the table, the more likely collisions get, and the
> more maintenance overhead is required to maintain free space and
> efficiency.
>
> Change-Id: I86e72510941969e7523df11f9e68926f46ef7af1
> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>

Acked-by: Christian König <christian.koenig at amd.com>

Please also send to the LKML cause that really needs a wider audience.

Regards,
Christian.

> ---
>   include/linux/chash.h | 349 +++++++++++++++++++++++++++++++++
>   lib/Kconfig           |   8 +
>   lib/Makefile          |   2 +
>   lib/chash.c           | 521 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 880 insertions(+)
>   create mode 100644 include/linux/chash.h
>   create mode 100644 lib/chash.c
>
> diff --git a/include/linux/chash.h b/include/linux/chash.h
> new file mode 100644
> index 0000000..3835575
> --- /dev/null
> +++ b/include/linux/chash.h
> @@ -0,0 +1,349 @@
> +/*
> + * Copyright 2017 Advanced Micro Devices, Inc.
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + *
> + */
> +
> +#ifndef _LINUX_CHASH_H
> +#define _LINUX_CHASH_H
> +
> +#include <linux/types.h>
> +#include <linux/hash.h>
> +#include <linux/bug.h>
> +#include <linux/bitops.h>
> +
> +struct __chash_table {
> +	u8 bits;
> +	u8 key_size;
> +	unsigned int value_size;
> +	u32 size_mask;
> +	unsigned long *occup_bitmap, *valid_bitmap;
> +	union {
> +		u32 *keys32;
> +		u64 *keys64;
> +	};
> +	u8 *values;
> +
> +#define CHASH_STATS
> +#ifdef CHASH_STATS
> +	u64 total_add_calls, total_add_steps;
> +	u64 total_find_calls, total_find_steps;
> +	u64 total_not_find_calls, total_not_find_steps;
> +	u64 total_relocations, total_relocation_distance;
> +#endif
> +};
> +
> +#define __CHASH_BITMAP_SIZE(bits)				\
> +	(((1 << (bits)) + BITS_PER_LONG - 1) / BITS_PER_LONG)
> +#define __CHASH_ARRAY_SIZE(bits, size)				\
> +	((((size) << (bits)) + sizeof(long) - 1) / sizeof(long))
> +
> +#define __CHASH_DATA_SIZE(bits, key_size, value_size)	\
> +	(__CHASH_BITMAP_SIZE(bits) * 2 +		\
> +	 __CHASH_ARRAY_SIZE(bits, key_size) +		\
> +	 __CHASH_ARRAY_SIZE(bits, value_size))
> +
> +#define STRUCT_CHASH_TABLE(bits, key_size, value_size)			\
> +	struct {							\
> +		struct __chash_table table;				\
> +		unsigned long data[					\
> +			__CHASH_DATA_SIZE(bits, key_size, value_size)];	\
> +	}
> +
> +/**
> + * struct chash_table - Dynamically allocated closed hash table
> + *
> + * Use this struct for dynamically allocated hash tables (using
> + * chash_table_alloc and chash_table_free), where the size is
> + * determined at runtime.
> + */
> +struct chash_table {
> +	struct __chash_table table;
> +	unsigned long *data;
> +};
> +
> +/**
> + * DECLARE_CHASH_TABLE - macro to declare a closed hash table
> + * @table: name of the declared hash table
> + * @bts: Table size will be 2^bits entries
> + * @key_sz: Size of hash keys in bytes, 4 or 8
> + * @val_sz: Size of data values in bytes, can be 0
> + *
> + * This declares the hash table variable with a static size.
> + *
> + * The closed hash table stores key-value pairs with low memory and
> + * lookup overhead. In operation it performs no dynamic memory
> + * management. The data being stored does not require any
> + * list_heads. The hash table performs best with small @val_sz and as
> + * long as some space (about 50%) is left free in the table. But the
> + * table can still work reasonably efficiently even when filled up to
> + * about 90%. If bigger data items need to be stored and looked up,
> + * store the pointer to it as value in the hash table.
> + *
> + * @val_sz may be 0. This can be useful when all the stored
> + * information is contained in the key itself and the fact that it is
> + * in the hash table (or not).
> + */
> +#define DECLARE_CHASH_TABLE(table, bts, key_sz, val_sz)		\
> +	STRUCT_CHASH_TABLE(bts, key_sz, val_sz) table
> +
> +#ifdef CHASH_STATS
> +#define __CHASH_STATS_INIT(prefix) ,			\
> +		prefix.total_add_calls = 0,		\
> +		prefix.total_add_steps = 0,		\
> +		prefix.total_find_calls = 0,		\
> +		prefix.total_find_steps = 0,		\
> +		prefix.total_not_find_calls = 0,	\
> +		prefix.total_not_find_steps = 0,	\
> +		prefix.total_relocations = 0,		\
> +		prefix.total_relocation_distance = 0
> +#else
> +#define __CHASH_STATS_INIT(prefix)
> +#endif
> +
> +#define __CHASH_TABLE_INIT(prefix, data, bts, key_sz, val_sz)	\
> +	prefix.bits = (bts),					\
> +		prefix.key_size = (key_sz),			\
> +		prefix.value_size = (val_sz),			\
> +		prefix.size_mask = ((1 << bts) - 1),		\
> +		prefix.occup_bitmap = &data[0],			\
> +		prefix.valid_bitmap = &data[			\
> +			__CHASH_BITMAP_SIZE(bts)],		\
> +		prefix.keys64 = (u64 *)&data[			\
> +			__CHASH_BITMAP_SIZE(bts) * 2],		\
> +		prefix.values = (u8 *)&data[			\
> +			__CHASH_BITMAP_SIZE(bts) * 2 +		\
> +			__CHASH_ARRAY_SIZE(bts, key_sz)]	\
> +		__CHASH_STATS_INIT(prefix)
> +
> +/**
> + * DEFINE_CHASH_TABLE - macro to define and initialize a closed hash table
> + * @tbl: name of the declared hash table
> + * @bts: Table size will be 2^bits entries
> + * @key_sz: Size of hash keys in bytes, 4 or 8
> + * @val_sz: Size of data values in bytes, can be 0
> + *
> + * Note: the macro can be used for global and local hash table variables.
> + */
> +#define DEFINE_CHASH_TABLE(tbl, bts, key_sz, val_sz)			\
> +	DECLARE_CHASH_TABLE(tbl, bts, key_sz, val_sz) = {		\
> +		.table = {						\
> +			__CHASH_TABLE_INIT(, (tbl).data, bts, key_sz, val_sz) \
> +		},							\
> +		.data = {0}						\
> +	}
> +
> +/**
> + * INIT_CHASH_TABLE - Initialize a hash table declared by DECLARE_CHASH_TABLE
> + * @tbl: name of the declared hash table
> + * @bts: Table size will be 2^bits entries
> + * @key_sz: Size of hash keys in bytes, 4 or 8
> + * @val_sz: Size of data values in bytes, can be 0
> + */
> +#define INIT_CHASH_TABLE(tbl, bts, key_sz, val_sz)			\
> +	__CHASH_TABLE_INIT(((tbl).table), (tbl).data, bts, key_sz, val_sz)
> +
> +int chash_table_alloc(struct chash_table *table, u8 bits, u8 key_size,
> +		      unsigned int value_size, gfp_t gfp_mask);
> +void chash_table_free(struct chash_table *table);
> +
> +/**
> + * chash_table_dump_stats - Dump statistics of a closed hash table
> + * @tbl: Pointer to the table structure
> + *
> + * Dumps some performance statistics of the table gathered in operation.
> + */
> +#ifdef CHASH_STATS
> +#define chash_table_dump_stats(tbl) __chash_table_dump_stats(&(*tbl).table)
> +
> +void __chash_table_dump_stats(struct __chash_table *table);
> +#else
> +#define chash_table_dump_stats(tbl)
> +#endif
> +
> +/**
> + * chash_table_copy_in - Copy a new value into the hash table
> + * @tbl: Pointer to the table structure
> + * @key: Key of the entry to add or update
> + * @value: Pointer to value to copy, may be NULL
> + *
> + * If @key already has an entry, its value is replaced. Otherwise a
> + * new entry is added. If @value is NULL, the value is left unchanged
> + * or uninitialized. Returns 1 if an entry already existed, 0 if a new
> + * entry was added or %-ENOMEM if there was no free space in the
> + * table.
> + */
> +#define chash_table_copy_in(tbl, key, value)			\
> +	__chash_table_copy_in(&(*tbl).table, key, value)
> +
> +int __chash_table_copy_in(struct __chash_table *table, u64 key,
> +			  const void *value);
> +
> +/**
> + * chash_table_copy_out - Copy a value out of the hash table
> + * @tbl: Pointer to the table structure
> + * @key: Key of the entry to find
> + * @value: Pointer to value to copy, may be NULL
> + *
> + * If @value is not NULL and the table has a non-0 value_size, the
> + * value at @key is copied to @value. Returns the slot index of the
> + * entry or %-EINVAL if @key was not found.
> + */
> +#define chash_table_copy_out(tbl, key, value)			\
> +	__chash_table_copy_out(&(*tbl).table, key, value, false)
> +
> +int __chash_table_copy_out(struct __chash_table *table, u64 key,
> +			   void *value, bool remove);
> +
> +/**
> + * chash_table_remove - Remove an entry from the hash table
> + * @tbl: Pointer to the table structure
> + * @key: Key of the entry to find
> + * @value: Pointer to value to copy, may be NULL
> + *
> + * If @value is not NULL and the table has a non-0 value_size, the
> + * value at @key is copied to @value. The entry is removed from the
> + * table. Returns the slot index of the removed entry or %-EINVAL if
> + * @key was not found.
> + */
> +#define chash_table_remove(tbl, key, value)			\
> +	__chash_table_copy_out(&(*tbl).table, key, value, true)
> +
> +#define CHASH_SELF_TEST
> +#ifdef CHASH_SELF_TEST
> +int chash_self_test(u8 bits, u8 key_size, int min_fill, int max_fill,
> +		    u64 iterations);
> +#endif
> +
> +/*
> + * Low level iterator API used internally by the above functions.
> + */
> +struct chash_iter {
> +	struct __chash_table *table;
> +	unsigned long mask;
> +	int slot;
> +};
> +
> +/**
> + * CHASH_ITER_INIT - Initialize a hash table iterator
> + * @tbl: Pointer to hash table to iterate over
> + * @s: Initial slot number
> + */
> +#define CHASH_ITER_INIT(table, s) {			\
> +		table,					\
> +		1UL << ((s) & (BITS_PER_LONG - 1)),	\
> +		s					\
> +	}
> +/**
> + * CHASH_ITER_SET - Set hash table iterator to new slot
> + * @iter: Iterator
> + * @s: Slot number
> + */
> +#define CHASH_ITER_SET(iter, s)					\
> +	(iter).mask = 1UL << ((s) & (BITS_PER_LONG - 1)),	\
> +	(iter).slot = (s)
> +/**
> + * CHASH_ITER_INC - Increment hash table iterator
> + * @table: Hash table to iterate over
> + *
> + * Wraps around at the end.
> + */
> +#define CHASH_ITER_INC(iter) do {					\
> +		(iter).mask = (iter).mask << 1 |			\
> +			(iter).mask >> (BITS_PER_LONG - 1);		\
> +		(iter).slot = ((iter).slot + 1) & (iter).table->size_mask; \
> +	} while (0)
> +
> +static inline bool chash_iter_is_valid(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	return !!(iter.table->valid_bitmap[iter.slot >> _BITOPS_LONG_SHIFT] &
> +		  iter.mask);
> +}
> +static inline bool chash_iter_is_empty(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	return !(iter.table->occup_bitmap[iter.slot >> _BITOPS_LONG_SHIFT] &
> +		 iter.mask);
> +}
> +
> +static inline void chash_iter_set_valid(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	iter.table->valid_bitmap[iter.slot >> _BITOPS_LONG_SHIFT] |= iter.mask;
> +	iter.table->occup_bitmap[iter.slot >> _BITOPS_LONG_SHIFT] |= iter.mask;
> +}
> +static inline void chash_iter_set_invalid(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	iter.table->valid_bitmap[iter.slot >> _BITOPS_LONG_SHIFT] &= ~iter.mask;
> +}
> +static inline void chash_iter_set_empty(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	iter.table->occup_bitmap[iter.slot >> _BITOPS_LONG_SHIFT] &= ~iter.mask;
> +}
> +
> +static inline u32 chash_iter_key32(const struct chash_iter iter)
> +{
> +	BUG_ON(iter.table->key_size != 4);
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	return iter.table->keys32[iter.slot];
> +}
> +static inline u64 chash_iter_key64(const struct chash_iter iter)
> +{
> +	BUG_ON(iter.table->key_size != 8);
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	return iter.table->keys64[iter.slot];
> +}
> +static inline u64 chash_iter_key(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	return (iter.table->key_size == 4) ?
> +		iter.table->keys32[iter.slot] : iter.table->keys64[iter.slot];
> +}
> +
> +static inline u32 chash_iter_hash32(const struct chash_iter iter)
> +{
> +	BUG_ON(iter.table->key_size != 4);
> +	return hash_32(chash_iter_key32(iter), iter.table->bits);
> +}
> +
> +static inline u32 chash_iter_hash64(const struct chash_iter iter)
> +{
> +	BUG_ON(iter.table->key_size != 8);
> +	return hash_64(chash_iter_key64(iter), iter.table->bits);
> +}
> +
> +static inline u32 chash_iter_hash(const struct chash_iter iter)
> +{
> +	return (iter.table->key_size == 4) ?
> +		hash_32(chash_iter_key32(iter), iter.table->bits) :
> +		hash_64(chash_iter_key64(iter), iter.table->bits);
> +}
> +
> +static inline void *chash_iter_value(const struct chash_iter iter)
> +{
> +	BUG_ON((unsigned)iter.slot >= (1 << iter.table->bits));
> +	return iter.table->values +
> +		((unsigned long)iter.slot * iter.table->value_size);
> +}
> +
> +#endif /* _LINUX_CHASH_H */
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 0c8b78a..e5e1438 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -564,4 +564,12 @@ config PARMAN
>   config PRIME_NUMBERS
>   	tristate
>   
> +#
> +# Closed hash table
> +#
> +config CHASH
> +	tristate "Closed hash table"
> +        help
> +	 Closed hash table implementation with low memory and CPU overhead.
> +
>   endmenu
> diff --git a/lib/Makefile b/lib/Makefile
> index 0166fbc..a44ec9f 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -243,3 +243,5 @@ UBSAN_SANITIZE_ubsan.o := n
>   obj-$(CONFIG_SBITMAP) += sbitmap.o
>   
>   obj-$(CONFIG_PARMAN) += parman.o
> +
> +obj-$(CONFIG_CHASH) += chash.o
> diff --git a/lib/chash.c b/lib/chash.c
> new file mode 100644
> index 0000000..08cdac1
> --- /dev/null
> +++ b/lib/chash.c
> @@ -0,0 +1,521 @@
> +/*
> + * Copyright 2017 Advanced Micro Devices, Inc.
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + *
> + */
> +
> +#include <linux/types.h>
> +#include <linux/hash.h>
> +#include <linux/bug.h>
> +#include <linux/slab.h>
> +#include <linux/module.h>
> +#include <linux/chash.h>
> +
> +/**
> + * chash_table_alloc - Allocate closed hash table
> + * @table: Pointer to the table structure
> + * @bits: Table size will be 2^bits entries
> + * @key_size: Size of hash keys in bytes, 4 or 8
> + * @value_size: Size of data values in bytes, can be 0
> + */
> +int chash_table_alloc(struct chash_table *table, u8 bits, u8 key_size,
> +		      unsigned value_size, gfp_t gfp_mask)
> +{
> +	if (bits > 31)
> +		return -EINVAL;
> +
> +	if (key_size != 4 && key_size != 8)
> +		return -EINVAL;
> +
> +	table->data = kcalloc(__CHASH_DATA_SIZE(bits, key_size, value_size),
> +		       sizeof(long), gfp_mask);
> +	if (!table->data)
> +		return -ENOMEM;
> +
> +	__CHASH_TABLE_INIT(table->table, table->data, bits, key_size, value_size);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(chash_table_alloc);
> +
> +/**
> + * chash_table_free - Free closed hash table
> + * @table: Pointer to the table structure
> + */
> +void chash_table_free(struct chash_table *table)
> +{
> +	kfree(table->data);
> +}
> +EXPORT_SYMBOL(chash_table_free);
> +
> +#ifdef CHASH_STATS
> +
> +#define DIV_FRAC(nom, denom, quot, frac, frac_digits) do {		\
> +		(quot) = (nom) / (denom);				\
> +		(frac) = ((nom) % (denom) * (frac_digits) +		\
> +			  (denom) / 2) / (denom);			\
> +	} while (0)
> +
> +void __chash_table_dump_stats(struct __chash_table *table)
> +{
> +	struct chash_iter iter = CHASH_ITER_INIT(table, 0);
> +	u32 filled = 0, empty = 0, tombstones = 0;
> +	u32 quot, frac;
> +	u32 quot2, frac2;
> +
> +	do {
> +		if (chash_iter_is_valid(iter))
> +			filled++;
> +		else if (chash_iter_is_empty(iter))
> +			empty++;
> +		else
> +			tombstones++;
> +		CHASH_ITER_INC(iter);
> +	} while (iter.slot);
> +
> +	pr_info("Hash table key size %d, value size %d\n",
> +		table->key_size, table->value_size);
> +	pr_info("  Slots total/filled/empty/tombstones: %u / %u / %u / %u\n",
> +		1 << table->bits, filled, empty, tombstones);
> +	pr_info("  Avg number of search steps for:\n");
> +	if (table->total_add_calls > 0)
> +		DIV_FRAC(table->total_add_steps, table->total_add_calls,
> +			 quot, frac, 1000);
> +	else
> +		quot = frac = 0;
> +	pr_info("    Add           : %u.%03u\n", quot, frac);
> +	if (table->total_find_calls > 0)
> +		DIV_FRAC(table->total_find_steps,
> +			 table->total_find_calls, quot, frac, 1000);
> +	else
> +		quot = frac = 0;
> +	if (table->total_not_find_calls > 0)
> +		DIV_FRAC(table->total_not_find_steps,
> +			 table->total_not_find_calls, quot2, frac2, 1000);
> +	else
> +		quot2 = frac2 = 0;
> +	pr_info("    Find(hit/miss): %u.%03u / %u.%03u\n", quot, frac, quot2, frac2);
> +	if (table->total_relocations) {
> +		u64 quot64;
> +
> +		DIV_FRAC(table->total_find_calls + table->total_not_find_calls,
> +			 table->total_relocations, quot64, frac, 1000);
> +		DIV_FRAC(table->total_relocation_distance,
> +			 table->total_relocations, quot2, frac2, 1000);
> +		pr_info("  Relocations (freq/avg.dist): 1:%llu.%03u / %u.%03u\n",
> +			quot64, frac, quot2, frac2);
> +	} else {
> +		pr_info("  No relocations\n");
> +	}
> +}
> +EXPORT_SYMBOL(__chash_table_dump_stats);
> +
> +#undef DIV_FRAC
> +#endif
> +
> +#define CHASH_INC(table, a) ((a) = ((a) + 1) & (table)->size_mask)
> +#define CHASH_ADD(table, a, b) (((a) + (b)) & (table)->size_mask)
> +#define CHASH_SUB(table, a, b) (((a) - (b)) & (table)->size_mask)
> +#define CHASH_IN_RANGE(table, slot, first, last) \
> +	(CHASH_SUB(table, slot, first) <= CHASH_SUB(table, last, first))
> +
> +/*#define CHASH_DEBUG Uncomment this to enable verbose debug output*/
> +#ifdef CHASH_DEBUG
> +static void chash_table_dump(struct __chash_table *table)
> +{
> +	struct chash_iter iter = CHASH_ITER_INIT(table, 0);
> +
> +	do {
> +		if ((iter.slot & 3) == 0)
> +			pr_debug("%04x: ", iter.slot);
> +
> +		if (chash_iter_is_valid(iter))
> +			pr_debug("[%016llx] ", chash_iter_key(iter));
> +		else if (chash_iter_is_empty(iter))
> +			pr_debug("[    <empty>     ] ");
> +		else
> +			pr_debug("[  <tombstone>   ] ");
> +
> +		if ((iter.slot & 3) == 3)
> +			pr_debug("\n");
> +
> +		CHASH_ITER_INC(iter);
> +	} while (iter.slot);
> +
> +	if ((iter.slot & 3) != 0)
> +		pr_debug("\n");
> +}
> +
> +static int chash_table_check(struct __chash_table *table)
> +{
> +	u32 hash;
> +	struct chash_iter iter = CHASH_ITER_INIT(table, 0);
> +	struct chash_iter cur = CHASH_ITER_INIT(table, 0);
> +
> +	do {
> +		if (!chash_iter_is_valid(iter)) {
> +			CHASH_ITER_INC(iter);
> +			continue;
> +		}
> +
> +		hash = chash_iter_hash(iter);
> +		CHASH_ITER_SET(cur, hash);
> +		while (cur.slot != iter.slot) {
> +			if (chash_iter_is_empty(cur)) {
> +				pr_err("Path to element at %x with hash %x broken at slot %x\n",
> +				       iter.slot, hash, cur.slot);
> +				chash_table_dump(table);
> +				return -EINVAL;
> +			}
> +			CHASH_ITER_INC(cur);
> +		}
> +
> +		CHASH_ITER_INC(iter);
> +	} while (iter.slot);
> +
> +	return 0;
> +}
> +#endif
> +
> +static void chash_iter_relocate(struct chash_iter dst, struct chash_iter src)
> +{
> +	BUG_ON(src.table == dst.table && src.slot == dst.slot);
> +	BUG_ON(src.table->key_size != src.table->key_size);
> +	BUG_ON(src.table->value_size != src.table->value_size);
> +
> +	if (dst.table->key_size == 4)
> +		dst.table->keys32[dst.slot] = src.table->keys32[src.slot];
> +	else
> +		dst.table->keys64[dst.slot] = src.table->keys64[src.slot];
> +
> +	if (dst.table->value_size)
> +		memcpy(chash_iter_value(dst), chash_iter_value(src),
> +		       dst.table->value_size);
> +
> +	chash_iter_set_valid(dst);
> +	chash_iter_set_invalid(src);
> +
> +#ifdef CHASH_STATS
> +	if (src.table == dst.table) {
> +		dst.table->total_relocations++;
> +		dst.table->total_relocation_distance +=
> +			CHASH_SUB(dst.table, src.slot, dst.slot);
> +	}
> +#endif
> +}
> +
> +/**
> + * __chash_table_find - Helper for looking up a hash table entry
> + * @iter: Pointer to hash table iterator
> + * @key: Key of the entry to find
> + * @for_removal: set to true if the element will be removed soon
> + *
> + * Searches for an entry in the hash table with a given key. iter must
> + * be initialized by the caller to point to the home position of the
> + * hypothetical entry, i.e. it must be initialized with the hash table
> + * and the key's hash as the initial slot for the search.
> + *
> + * This function also does some local clean-up to speed up future
> + * look-ups by relocating entries to better slots and removing
> + * tombstones that are no longer needed.
> + *
> + * If @for_removal is true, the function avoids relocating the entry
> + * that is being returned.
> + *
> + * Returns 0 if the search is successful. In this case iter is updated
> + * to point to the found entry. Otherwise %-EINVAL is returned and the
> + * iter is updated to point to the first available slot for the given
> + * key. If the table is full, the slot is set to -1.
> + */
> +static int chash_table_find(struct chash_iter *iter, u64 key,
> +			    bool for_removal)
> +{
> +	u32 hash = iter->slot;
> +	struct chash_iter first_redundant = CHASH_ITER_INIT(iter->table, -1);
> +	int first_avail = (for_removal ? -2 : -1);
> +
> +	while (!chash_iter_is_valid(*iter) || chash_iter_key(*iter) != key) {
> +		if (chash_iter_is_empty(*iter)) {
> +			/* Found an empty slot, which ends the
> +			 * search. Clean up any preceding tombstones
> +			 * that are no longer needed because they lead
> +			 * to no-where
> +			 */
> +			if ((int)first_redundant.slot < 0)
> +				goto not_found;
> +			while (first_redundant.slot != iter->slot) {
> +				if (!chash_iter_is_valid(first_redundant))
> +					chash_iter_set_empty(first_redundant);
> +				CHASH_ITER_INC(first_redundant);
> +			}
> +#ifdef CHASH_DEBUG
> +			chash_table_check(iter->table);
> +#endif
> +			goto not_found;
> +		} else if (!chash_iter_is_valid(*iter)) {
> +			/* Found a tombstone. Remember it as candidate
> +			 * for relocating the entry we're looking for
> +			 * or for adding a new entry with the given key
> +			 */
> +			if (first_avail == -1)
> +				first_avail = iter->slot;
> +			/* Or mark it as the start of a series of
> +			 * potentially redundant tombstones
> +			 */
> +			else if (first_redundant.slot == -1)
> +				CHASH_ITER_SET(first_redundant, iter->slot);
> +		} else if (first_redundant.slot >= 0) {
> +			/* Found a valid, occupied slot with a
> +			 * preceding series of tombstones. Relocate it
> +			 * to a better position that no longer depends
> +			 * on those tombstones
> +			 */
> +			u32 cur_hash = chash_iter_hash(*iter);
> +
> +			if (!CHASH_IN_RANGE(iter->table, cur_hash,
> +					    first_redundant.slot + 1,
> +					    iter->slot)) {
> +				/* This entry has a hash at or before
> +				 * the first tombstone we found. We
> +				 * can relocate it to that tombstone
> +				 * and advance to the next tombstone
> +				 */
> +				chash_iter_relocate(first_redundant, *iter);
> +				do {
> +					CHASH_ITER_INC(first_redundant);
> +				} while (chash_iter_is_valid(first_redundant));
> +			} else if (cur_hash != iter->slot) {
> +				/* Relocate entry to its home position
> +				 * or a close as possible so it no
> +				 * longer depends on any preceding
> +				 * tombstones
> +				 */
> +				struct chash_iter new_iter =
> +					CHASH_ITER_INIT(iter->table, cur_hash);
> +
> +				while (new_iter.slot != iter->slot &&
> +				       chash_iter_is_valid(new_iter))
> +					CHASH_ITER_INC(new_iter);
> +
> +				if (new_iter.slot != iter->slot)
> +					chash_iter_relocate(new_iter, *iter);
> +			}
> +		}
> +
> +		CHASH_ITER_INC(*iter);
> +		if (iter->slot == hash) {
> +			iter->slot = -1;
> +			goto not_found;
> +		}
> +	}
> +
> +#ifdef CHASH_STATS
> +	iter->table->total_find_calls++;
> +	iter->table->total_find_steps +=
> +		CHASH_SUB(iter->table, iter->slot, hash) + 1;
> +#endif
> +
> +	if (first_avail >= 0) {
> +		CHASH_ITER_SET(first_redundant, first_avail);
> +		chash_iter_relocate(first_redundant, *iter);
> +		iter->slot = first_redundant.slot;
> +		iter->mask = first_redundant.mask;
> +	}
> +
> +	return 0;
> +
> +not_found:
> +#ifdef CHASH_STATS
> +	iter->table->total_not_find_calls++;
> +	iter->table->total_not_find_steps += (iter->slot < 0) ?
> +		(1 << iter->table->bits) :
> +		CHASH_SUB(iter->table, iter->slot, hash) + 1;
> +#endif
> +	if (first_avail >= 0)
> +		CHASH_ITER_SET(*iter, first_avail);
> +	return -EINVAL;
> +}
> +
> +int __chash_table_copy_in(struct __chash_table *table, u64 key,
> +			  const void *value)
> +{
> +	u32 hash = (table->key_size == 4) ?
> +		hash_32(key, table->bits) : hash_64(key, table->bits);
> +	struct chash_iter iter = CHASH_ITER_INIT(table, hash);
> +	int r = chash_table_find(&iter, key, false);
> +
> +	/* Found an existing entry */
> +	if (!r) {
> +		if (value && table->value_size)
> +			memcpy(chash_iter_value(iter), value,
> +			       table->value_size);
> +		return 1;
> +	}
> +
> +	/* Is there a place to add a new entry? */
> +	if (iter.slot < 0) {
> +		pr_err("Hash table overflow\n");
> +		return -ENOMEM;
> +	}
> +
> +	chash_iter_set_valid(iter);
> +
> +	if (table->key_size == 4)
> +		table->keys32[iter.slot] = key;
> +	else
> +		table->keys64[iter.slot] = key;
> +	if (value && table->value_size)
> +		memcpy(chash_iter_value(iter), value, table->value_size);
> +
> +#ifdef CHASH_STATS
> +	table->total_add_calls++;
> +	table->total_add_steps += CHASH_SUB(table, iter.slot, hash) + 1;
> +#endif
> +	return 0;
> +}
> +EXPORT_SYMBOL(__chash_table_copy_in);
> +
> +int __chash_table_copy_out(struct __chash_table *table, u64 key,
> +			   void *value, bool remove)
> +{
> +	u32 hash = (table->key_size == 4) ?
> +		hash_32(key, table->bits) : hash_64(key, table->bits);
> +	struct chash_iter iter = CHASH_ITER_INIT(table, hash);
> +	int r = chash_table_find(&iter, key, remove);
> +
> +	if (r < 0)
> +		return r;
> +
> +	if (value && table->value_size)
> +		memcpy(value, chash_iter_value(iter), table->value_size);
> +
> +	if (remove)
> +		chash_iter_set_invalid(iter);
> +
> +	return iter.slot;
> +}
> +EXPORT_SYMBOL(__chash_table_copy_out);
> +
> +#ifdef CHASH_SELF_TEST
> +/**
> + * chash_self_test - Run a self-test of the hash table implementation
> + * @bits: Table size will be 2^bits entries
> + * @key_size: Size of hash keys in bytes, 4 or 8
> + * @min_fill: Minimum fill level during the test
> + * @max_fill: Maximum fill level during the test
> + * @iterations: Number of test iterations
> + *
> + * The test adds and removes entries from a hash table, cycling the
> + * fill level between min_fill and max_fill entries. Also tests lookup
> + * and value retrieval.
> + */
> +int chash_self_test(u8 bits, u8 key_size, int min_fill, int max_fill,
> +		    u64 iterations)
> +{
> +	struct chash_table table;
> +	int ret;
> +	u64 add_count, rmv_count;
> +	u64 value;
> +
> +	if (key_size == 4 && iterations > 0xffffffff)
> +		return -EINVAL;
> +	if (min_fill >= max_fill)
> +		return -EINVAL;
> +
> +	ret = chash_table_alloc(&table, bits, key_size, sizeof(u64),
> +				GFP_KERNEL);
> +	if (ret) {
> +		pr_err("chash_table_alloc failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	for (add_count = 0, rmv_count = 0; add_count < iterations;
> +	     add_count++) {
> +		/* When we hit the max_fill level, remove entries down
> +		 * to min_fill */
> +		if (add_count - rmv_count == max_fill) {
> +			u64 find_count = rmv_count;
> +
> +			/* First try to find all entries that we're
> +			 * about to remove, confirm their value, test
> +			 * writing them back a second time. */
> +			for (; add_count - find_count > min_fill;
> +			     find_count++) {
> +				ret = chash_table_copy_out(&table, find_count,
> +							   &value);
> +				if (ret < 0) {
> +					pr_err("chash_table_copy_out failed: %d\n",
> +					       ret);
> +					goto out;
> +				}
> +				if (value != ~find_count) {
> +					pr_err("Wrong value retrieved for key 0x%llx, expected 0x%llx got 0x%llx\n",
> +					       find_count, ~find_count, value);
> +#ifdef CHASH_DEBUG
> +					chash_table_dump(&table.table);
> +#endif
> +					ret = -EFAULT;
> +					goto out;
> +				}
> +				ret = chash_table_copy_in(&table, find_count,
> +							  &value);
> +				if (ret != 1) {
> +					pr_err("copy_in second time returned %d, expected 1\n",
> +					       ret);
> +					ret = -EFAULT;
> +					goto out;
> +				}
> +			}
> +			/* Remove them until we hit min_fill level */
> +			for (; add_count - rmv_count > min_fill; rmv_count++) {
> +				ret = chash_table_remove(&table, rmv_count, NULL);
> +				if (ret < 0) {
> +					pr_err("chash_table_remove failed: %d\n",
> +					       ret);
> +					goto out;
> +				}
> +			}
> +		}
> +
> +		/* Add a new value */
> +		value = ~add_count;
> +		ret = chash_table_copy_in(&table, add_count, &value);
> +		if (ret != 0) {
> +			pr_err("copy_in first time returned %d, expected 0\n",
> +			       ret);
> +			ret = -EFAULT;
> +			goto out;
> +		}
> +	}
> +
> +#ifdef CHASH_STATS
> +	chash_table_dump_stats(&table);
> +#endif
> +
> +out:
> +	chash_table_free(&table);
> +	return ret;
> +}
> +EXPORT_SYMBOL(chash_self_test);
> +
> +#endif /* CHASH_SELF_TEST */
> +
> +MODULE_DESCRIPTION("Closed hash table");
> +MODULE_LICENSE("GPL and additional rights");




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