[PATCH] lib: Closed hash table with low overhead

[Felix Kuehling]

This adds a statically sized 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.
Static memory usage per entry comprises a 32 or 64 bit hash key, two
bits for occupancy tracking and the value size stored in the table.
No list heads or pointers are needed. Therefore this data structure
should be quite cache-friendly, too.

It uses linear probing and lazy deletion. During lookups free space
is reclaimed and entries relocated to speed up future lookups.

Signed-off-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Acked-by: Christian KÃnig <christian.koenig@xxxxxxx>
---

This is part of a larger patch series I'm working on to support
demand-paging on AMD Vega10 and similar AMD GPUs. Vega10 generates a
flood of page fault events in its interrupt ring buffer for every
retry. I need a very fast way to discard known page faults in the
interrupt handler to stop processing retry events as early as
possible.

I don't actually need to store any data. All the information I need is
in the hash key itself, which is made up of the fault address and
process ID. I don't need a dynamically resizable data structure
because the hardware will keep retrying. If my hashtable fills up, I
can just discard retry events indiscriminately until space is freed
(by handling older page faults).

In preliminary testing with the builtin self test on a 3.6GHz Core i7,
this code can manage over 120M lookups per second (hits, misses take
about twice as long) with the table 40-50% full. Even 80-90% full it
still remains quite efficient with hits still almost as fast but
misses taking 8x as long as misses.

I'm hoping that people find this useful and consider including it as a
library routine in the kernel.

 include/linux/chash.h | 358 +++++++++++++++++++++++++++++
 lib/Kconfig           |  24 ++
 lib/Makefile          |   2 +
 lib/chash.c           | 622 ++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 1006 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..c89b92b
--- /dev/null
+++ b/include/linux/chash.h
@@ -0,0 +1,358 @@
+/*
+ * 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;
+
+#ifdef CONFIG_CHASH_STATS
+	u64 hits, hits_steps, hits_time_ns;
+	u64 miss, miss_steps, miss_time_ns;
+	u64 relocs, reloc_dist;
+#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 CONFIG_CHASH_STATS
+#define __CHASH_STATS_INIT(prefix),		\
+		prefix.hits = 0,		\
+		prefix.hits_steps = 0,		\
+		prefix.hits_time_ns = 0,	\
+		prefix.miss = 0,		\
+		prefix.miss_steps = 0,		\
+		prefix.miss_time_ns = 0,	\
+		prefix.relocs = 0,		\
+		prefix.reloc_dist = 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
+ * in the kernel log using pr_debug. If CONFIG_DYNAMIC_DEBUG is enabled,
+ * user must turn on messages for chash.c (file chash.c +p).
+ */
+#ifdef CONFIG_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_reset_stats - Reset statistics of a closed hash table
+ * @tbl: Pointer to the table structure
+ */
+#ifdef CONFIG_CHASH_STATS
+#define chash_table_reset_stats(tbl) __chash_table_reset_stats(&(*tbl).table)
+
+static inline void __chash_table_reset_stats(struct __chash_table *table)
+{
+	(void)table __CHASH_STATS_INIT((*table));
+}
+#else
+#define chash_table_reset_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)
+
+/*
+ * 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 6762529..9e49129 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -575,4 +575,28 @@ config PARMAN
 config PRIME_NUMBERS
 	tristate
 
+#
+# Closed hash table
+#
+config CHASH
+	tristate "Closed hash table"
+	help
+	 Statically sized closed hash table implementation with low
+	 memory and CPU overhead.
+
+config CHASH_STATS
+	bool "Closed hash table performance statistics"
+	depends on CHASH
+	default n
+	help
+	 Enable collection of performance statistics for closed hash tables.
+
+config CHASH_SELFTEST
+	bool "Closed hash table self test"
+	depends on CHASH
+	default n
+	help
+	 Runs a selftest during module load. Several module parameters
+	 are available to modify the behaviour of the test.
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 40c1837..c332ed9 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..1bc4287
--- /dev/null
+++ b/lib/chash.c
@@ -0,0 +1,622 @@
+/*
+ * 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/sched/clock.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 int 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 CONFIG_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;
+	u64 quot1, quot2;
+	u32 frac1, 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_debug("chash: key size %u, value size %u\n",
+		 table->key_size, table->value_size);
+	pr_debug("  Slots total/filled/empty/tombstones: %u / %u / %u / %u\n",
+		 1 << table->bits, filled, empty, tombstones);
+	if (table->hits > 0) {
+		DIV_FRAC(table->hits_steps, table->hits, quot1, frac1, 1000);
+		DIV_FRAC(table->hits * 1000, table->hits_time_ns,
+			 quot2, frac2, 1000);
+	} else {
+		quot1 = quot2 = 0;
+		frac1 = frac2 = 0;
+	}
+	pr_debug("  Hits   (avg.cost, rate): %llu (%llu.%03u, %llu.%03u M/s)\n",
+		 table->hits, quot1, frac1, quot2, frac2);
+	if (table->miss > 0) {
+		DIV_FRAC(table->miss_steps, table->miss, quot1, frac1, 1000);
+		DIV_FRAC(table->miss * 1000, table->miss_time_ns,
+			 quot2, frac2, 1000);
+	} else {
+		quot1 = quot2 = 0;
+		frac1 = frac2 = 0;
+	}
+	pr_debug("  Misses (avg.cost, rate): %llu (%llu.%03u, %llu.%03u M/s)\n",
+		 table->miss, quot1, frac1, quot2, frac2);
+	if (table->hits + table->miss > 0) {
+		DIV_FRAC(table->hits_steps + table->miss_steps,
+			 table->hits + table->miss, quot1, frac1, 1000);
+		DIV_FRAC((table->hits + table->miss) * 1000,
+			 (table->hits_time_ns + table->miss_time_ns),
+			 quot2, frac2, 1000);
+	} else {
+		quot1 = quot2 = 0;
+		frac1 = frac2 = 0;
+	}
+	pr_debug("  Total  (avg.cost, rate): %llu (%llu.%03u, %llu.%03u M/s)\n",
+		 table->hits + table->miss, quot1, frac1, quot2, frac2);
+	if (table->relocs > 0) {
+		DIV_FRAC(table->hits + table->miss, table->relocs,
+			 quot1, frac1, 1000);
+		DIV_FRAC(table->reloc_dist, table->relocs, quot2, frac2, 1000);
+		pr_debug("  Relocations (freq, avg.dist): %llu (1:%llu.%03u, %llu.%03u)\n",
+			 table->relocs, quot1, frac1, quot2, frac2);
+	} else {
+		pr_debug("  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 CONFIG_CHASH_STATS
+	if (src.table == dst.table) {
+		dst.table->relocs++;
+		dst.table->reloc_dist +=
+			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)
+{
+#ifdef CONFIG_CHASH_STATS
+	u64 ts1 = local_clock();
+#endif
+	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 as 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 CONFIG_CHASH_STATS
+	iter->table->hits++;
+	iter->table->hits_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;
+	}
+
+#ifdef CONFIG_CHASH_STATS
+	iter->table->hits_time_ns += local_clock() - ts1;
+#endif
+
+	return 0;
+
+not_found:
+#ifdef CONFIG_CHASH_STATS
+	iter->table->miss++;
+	iter->table->miss_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);
+
+#ifdef CONFIG_CHASH_STATS
+	iter->table->miss_time_ns += local_clock() - ts1;
+#endif
+
+	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);
+
+	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 CONFIG_CHASH_SELFTEST
+/**
+ * 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.
+ */
+static int __init 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;
+		}
+	}
+
+	chash_table_dump_stats(&table);
+	chash_table_reset_stats(&table);
+
+out:
+	chash_table_free(&table);
+	return ret;
+}
+
+static unsigned int chash_test_bits = 10;
+MODULE_PARM_DESC(test_bits,
+		 "Selftest number of hash bits ([4..20], default=10)");
+module_param_named(test_bits, chash_test_bits, uint, 0444);
+
+static unsigned int chash_test_keysize = 8;
+MODULE_PARM_DESC(test_keysize, "Selftest keysize (4 or 8, default=8)");
+module_param_named(test_keysize, chash_test_keysize, uint, 0444);
+
+static unsigned int chash_test_minfill;
+MODULE_PARM_DESC(test_minfill, "Selftest minimum #entries (default=50%)");
+module_param_named(test_minfill, chash_test_minfill, uint, 0444);
+
+static unsigned int chash_test_maxfill;
+MODULE_PARM_DESC(test_maxfill, "Selftest maximum #entries (default=80%)");
+module_param_named(test_maxfill, chash_test_maxfill, uint, 0444);
+
+static unsigned long chash_test_iters;
+MODULE_PARM_DESC(test_iters, "Selftest iterations (default=1000 x #entries)");
+module_param_named(test_iters, chash_test_iters, ulong, 0444);
+
+static int __init chash_init(void)
+{
+	int ret;
+	u64 ts1_ns, ts_delta_us;
+
+	/* Skip self test on user errors */
+	if (chash_test_bits < 4 || chash_test_bits > 20) {
+		pr_err("chash: test_bits out of range [4..20].\n");
+		return 0;
+	}
+	if (chash_test_keysize != 4 && chash_test_keysize != 8) {
+		pr_err("chash: test_keysize invalid. Must be 4 or 8.\n");
+		return 0;
+	}
+
+	if (!chash_test_minfill)
+		chash_test_minfill = (1 << chash_test_bits) / 2;
+	if (!chash_test_maxfill)
+		chash_test_maxfill = (1 << chash_test_bits) * 4 / 5;
+	if (!chash_test_iters)
+		chash_test_iters = (1 << chash_test_bits) * 1000;
+
+	if (chash_test_minfill >= (1 << chash_test_bits)) {
+		pr_err("chash: test_minfill too big. Must be < table size.\n");
+		return 0;
+	}
+	if (chash_test_maxfill >= (1 << chash_test_bits)) {
+		pr_err("chash: test_maxfill too big. Must be < table size.\n");
+		return 0;
+	}
+	if (chash_test_minfill >= chash_test_maxfill) {
+		pr_err("chash: test_minfill must be < test_maxfill.\n");
+		return 0;
+	}
+	if (chash_test_keysize == 4 && chash_test_iters > 0xffffffff) {
+		pr_err("chash: test_iters must be < 4G for 4 byte keys.\n");
+		return 0;
+	}
+
+	ts1_ns = local_clock();
+	ret = chash_self_test(chash_test_bits, chash_test_keysize,
+			      chash_test_minfill, chash_test_maxfill,
+			      chash_test_iters);
+	if (!ret) {
+		ts_delta_us = (local_clock() - ts1_ns) / 1000;
+		pr_info("chash: self test took %llu us, %llu iterations/s\n",
+			ts_delta_us,
+			(u64)chash_test_iters * 1000000 / ts_delta_us);
+	} else {
+		pr_err("chash: self test failed: %d\n", ret);
+	}
+
+	return ret;
+}
+
+module_init(chash_init);
+
+#endif /* CONFIG_CHASH_SELFTEST */
+
+MODULE_DESCRIPTION("Closed hash table");
+MODULE_LICENSE("GPL and additional rights");
-- 
2.7.4