lib/lru_cache.c - kernel/msm - Gitiles

 /*
    lru_cache.c

    This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

    Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
    Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
    Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.

    drbd is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2, or (at your option)
    any later version.

    drbd is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with drbd; see the file COPYING.  If not, write to
    the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

  */

 #include <linux/module.h>
 #include <linux/bitops.h>
 #include <linux/slab.h>
 #include <linux/string.h> /* for memset */
 #include <linux/seq_file.h> /* for seq_printf */
 #include <linux/lru_cache.h>

 MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
 	      "Lars Ellenberg <lars@linbit.com>");
 MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
 MODULE_LICENSE("GPL");

 /* this is developers aid only.
  * it catches concurrent access (lack of locking on the users part) */
 #define PARANOIA_ENTRY() do {		\
 	BUG_ON(!lc);			\
 	BUG_ON(!lc->nr_elements);	\
 	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
 } while (0)

 #define RETURN(x...)     do { \
 	clear_bit(__LC_PARANOIA, &lc->flags); \
 	smp_mb__after_clear_bit(); return x ; } while (0)

 /* BUG() if e is not one of the elements tracked by lc */
 #define PARANOIA_LC_ELEMENT(lc, e) do {	\
 	struct lru_cache *lc_ = (lc);	\
 	struct lc_element *e_ = (e);	\
 	unsigned i = e_->lc_index;	\
 	BUG_ON(i >= lc_->nr_elements);	\
 	BUG_ON(lc_->lc_element[i] != e_); } while (0)

 /**
  * lc_create - prepares to track objects in an active set
  * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
  * @e_count: number of elements allowed to be active simultaneously
  * @e_size: size of the tracked objects
  * @e_off: offset to the &struct lc_element member in a tracked object
  *
  * Returns a pointer to a newly initialized struct lru_cache on success,
  * or NULL on (allocation) failure.
  */
 struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
 		unsigned e_count, size_t e_size, size_t e_off)
 {
 	struct hlist_head *slot = NULL;
 	struct lc_element **element = NULL;
 	struct lru_cache *lc;
 	struct lc_element *e;
 	unsigned cache_obj_size = kmem_cache_size(cache);
 	unsigned i;

 	WARN_ON(cache_obj_size < e_size);
 	if (cache_obj_size < e_size)
 		return NULL;

 	/* e_count too big; would probably fail the allocation below anyways.
 	 * for typical use cases, e_count should be few thousand at most. */
 	if (e_count > LC_MAX_ACTIVE)
 		return NULL;

 	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
 	if (!slot)
 		goto out_fail;
 	element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
 	if (!element)
 		goto out_fail;

 	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
 	if (!lc)
 		goto out_fail;

 	INIT_LIST_HEAD(&lc->in_use);
 	INIT_LIST_HEAD(&lc->lru);
 	INIT_LIST_HEAD(&lc->free);

 	lc->name = name;
 	lc->element_size = e_size;
 	lc->element_off = e_off;
 	lc->nr_elements = e_count;
 	lc->new_number = LC_FREE;
 	lc->lc_cache = cache;
 	lc->lc_element = element;
 	lc->lc_slot = slot;

 	/* preallocate all objects */
 	for (i = 0; i < e_count; i++) {
 		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
 		if (!p)
 			break;
 		memset(p, 0, lc->element_size);
 		e = p + e_off;
 		e->lc_index = i;
 		e->lc_number = LC_FREE;
 		list_add(&e->list, &lc->free);
 		element[i] = e;
 	}
 	if (i == e_count)
 		return lc;

 	/* else: could not allocate all elements, give up */
 	for (i--; i; i--) {
 		void *p = element[i];
 		kmem_cache_free(cache, p - e_off);
 	}
 	kfree(lc);
 out_fail:
 	kfree(element);
 	kfree(slot);
 	return NULL;
 }

 void lc_free_by_index(struct lru_cache *lc, unsigned i)
 {
 	void *p = lc->lc_element[i];
 	WARN_ON(!p);
 	if (p) {
 		p -= lc->element_off;
 		kmem_cache_free(lc->lc_cache, p);
 	}
 }

 /**
  * lc_destroy - frees memory allocated by lc_create()
  * @lc: the lru cache to destroy
  */
 void lc_destroy(struct lru_cache *lc)
 {
 	unsigned i;
 	if (!lc)
 		return;
 	for (i = 0; i < lc->nr_elements; i++)
 		lc_free_by_index(lc, i);
 	kfree(lc->lc_element);
 	kfree(lc->lc_slot);
 	kfree(lc);
 }

 /**
  * lc_reset - does a full reset for @lc and the hash table slots.
  * @lc: the lru cache to operate on
  *
  * It is roughly the equivalent of re-allocating a fresh lru_cache object,
  * basically a short cut to lc_destroy(lc); lc = lc_create(...);
  */
 void lc_reset(struct lru_cache *lc)
 {
 	unsigned i;

 	INIT_LIST_HEAD(&lc->in_use);
 	INIT_LIST_HEAD(&lc->lru);
 	INIT_LIST_HEAD(&lc->free);
 	lc->used = 0;
 	lc->hits = 0;
 	lc->misses = 0;
 	lc->starving = 0;
 	lc->dirty = 0;
 	lc->changed = 0;
 	lc->flags = 0;
 	lc->changing_element = NULL;
 	lc->new_number = LC_FREE;
 	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);

 	for (i = 0; i < lc->nr_elements; i++) {
 		struct lc_element *e = lc->lc_element[i];
 		void *p = e;
 		p -= lc->element_off;
 		memset(p, 0, lc->element_size);
 		/* re-init it */
 		e->lc_index = i;
 		e->lc_number = LC_FREE;
 		list_add(&e->list, &lc->free);
 	}
 }

 /**
  * lc_seq_printf_stats - print stats about @lc into @seq
  * @seq: the seq_file to print into
  * @lc: the lru cache to print statistics of
  */
 size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
 {
 	/* NOTE:
 	 * total calls to lc_get are
 	 * (starving + hits + misses)
 	 * misses include "dirty" count (update from an other thread in
 	 * progress) and "changed", when this in fact lead to an successful
 	 * update of the cache.
 	 */
 	return seq_printf(seq, "\t%s: used:%u/%u "
 		"hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n",
 		lc->name, lc->used, lc->nr_elements,
 		lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed);
 }

 static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
 {
 	return  lc->lc_slot + (enr % lc->nr_elements);
 }


 /**
  * lc_find - find element by label, if present in the hash table
  * @lc: The lru_cache object
  * @enr: element number
  *
  * Returns the pointer to an element, if the element with the requested
  * "label" or element number is present in the hash table,
  * or NULL if not found. Does not change the refcnt.
  */
 struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
 {
 	struct hlist_node *n;
 	struct lc_element *e;

 	BUG_ON(!lc);
 	BUG_ON(!lc->nr_elements);
 	hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) {
 		if (e->lc_number == enr)
 			return e;
 	}
 	return NULL;
 }

 /* returned element will be "recycled" immediately */
 static struct lc_element *lc_evict(struct lru_cache *lc)
 {
 	struct list_head  *n;
 	struct lc_element *e;

 	if (list_empty(&lc->lru))
 		return NULL;

 	n = lc->lru.prev;
 	e = list_entry(n, struct lc_element, list);

 	PARANOIA_LC_ELEMENT(lc, e);

 	list_del(&e->list);
 	hlist_del(&e->colision);
 	return e;
 }

 /**
  * lc_del - removes an element from the cache
  * @lc: The lru_cache object
  * @e: The element to remove
  *
  * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
  * sets @e->enr to %LC_FREE.
  */
 void lc_del(struct lru_cache *lc, struct lc_element *e)
 {
 	PARANOIA_ENTRY();
 	PARANOIA_LC_ELEMENT(lc, e);
 	BUG_ON(e->refcnt);

 	e->lc_number = LC_FREE;
 	hlist_del_init(&e->colision);
 	list_move(&e->list, &lc->free);
 	RETURN();
 }

 static struct lc_element *lc_get_unused_element(struct lru_cache *lc)
 {
 	struct list_head *n;

 	if (list_empty(&lc->free))
 		return lc_evict(lc);

 	n = lc->free.next;
 	list_del(n);
 	return list_entry(n, struct lc_element, list);
 }

 static int lc_unused_element_available(struct lru_cache *lc)
 {
 	if (!list_empty(&lc->free))
 		return 1; /* something on the free list */
 	if (!list_empty(&lc->lru))
 		return 1;  /* something to evict */

 	return 0;
 }


 /**
  * lc_get - get element by label, maybe change the active set
  * @lc: the lru cache to operate on
  * @enr: the label to look up
  *
  * Finds an element in the cache, increases its usage count,
  * "touches" and returns it.
  *
  * In case the requested number is not present, it needs to be added to the
  * cache. Therefore it is possible that an other element becomes evicted from
  * the cache. In either case, the user is notified so he is able to e.g. keep
  * a persistent log of the cache changes, and therefore the objects in use.
  *
  * Return values:
  *  NULL
  *     The cache was marked %LC_STARVING,
  *     or the requested label was not in the active set
  *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
  *     Or no unused or free element could be recycled (@lc will be marked as
  *     %LC_STARVING, blocking further lc_get() operations).
  *
  *  pointer to the element with the REQUESTED element number.
  *     In this case, it can be used right away
  *
  *  pointer to an UNUSED element with some different element number,
  *          where that different number may also be %LC_FREE.
  *
  *          In this case, the cache is marked %LC_DIRTY (blocking further changes),
  *          and the returned element pointer is removed from the lru list and
  *          hash collision chains.  The user now should do whatever housekeeping
  *          is necessary.
  *          Then he must call lc_changed(lc,element_pointer), to finish
  *          the change.
  *
  * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
  *       any cache set change.
  */
 struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
 {
 	struct lc_element *e;

 	PARANOIA_ENTRY();
 	if (lc->flags & LC_STARVING) {
 		++lc->starving;
 		RETURN(NULL);
 	}

 	e = lc_find(lc, enr);
 	if (e) {
 		++lc->hits;
 		if (e->refcnt++ == 0)
 			lc->used++;
 		list_move(&e->list, &lc->in_use); /* Not evictable... */
 		RETURN(e);
 	}

 	++lc->misses;

 	/* In case there is nothing available and we can not kick out
 	 * the LRU element, we have to wait ...
 	 */
 	if (!lc_unused_element_available(lc)) {
 		__set_bit(__LC_STARVING, &lc->flags);
 		RETURN(NULL);
 	}

 	/* it was not present in the active set.
 	 * we are going to recycle an unused (or even "free") element.
 	 * user may need to commit a transaction to record that change.
 	 * we serialize on flags & TF_DIRTY */
 	if (test_and_set_bit(__LC_DIRTY, &lc->flags)) {
 		++lc->dirty;
 		RETURN(NULL);
 	}

 	e = lc_get_unused_element(lc);
 	BUG_ON(!e);

 	clear_bit(__LC_STARVING, &lc->flags);
 	BUG_ON(++e->refcnt != 1);
 	lc->used++;

 	lc->changing_element = e;
 	lc->new_number = enr;

 	RETURN(e);
 }

 /* similar to lc_get,
  * but only gets a new reference on an existing element.
  * you either get the requested element, or NULL.
  * will be consolidated into one function.
  */
 struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
 {
 	struct lc_element *e;

 	PARANOIA_ENTRY();
 	if (lc->flags & LC_STARVING) {
 		++lc->starving;
 		RETURN(NULL);
 	}

 	e = lc_find(lc, enr);
 	if (e) {
 		++lc->hits;
 		if (e->refcnt++ == 0)
 			lc->used++;
 		list_move(&e->list, &lc->in_use); /* Not evictable... */
 	}
 	RETURN(e);
 }

 /**
  * lc_changed - tell @lc that the change has been recorded
  * @lc: the lru cache to operate on
  * @e: the element pending label change
  */
 void lc_changed(struct lru_cache *lc, struct lc_element *e)
 {
 	PARANOIA_ENTRY();
 	BUG_ON(e != lc->changing_element);
 	PARANOIA_LC_ELEMENT(lc, e);
 	++lc->changed;
 	e->lc_number = lc->new_number;
 	list_add(&e->list, &lc->in_use);
 	hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number));
 	lc->changing_element = NULL;
 	lc->new_number = LC_FREE;
 	clear_bit(__LC_DIRTY, &lc->flags);
 	smp_mb__after_clear_bit();
 	RETURN();
 }


 /**
  * lc_put - give up refcnt of @e
  * @lc: the lru cache to operate on
  * @e: the element to put
  *
  * If refcnt reaches zero, the element is moved to the lru list,
  * and a %LC_STARVING (if set) is cleared.
  * Returns the new (post-decrement) refcnt.
  */
 unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
 {
 	PARANOIA_ENTRY();
 	PARANOIA_LC_ELEMENT(lc, e);
 	BUG_ON(e->refcnt == 0);
 	BUG_ON(e == lc->changing_element);
 	if (--e->refcnt == 0) {
 		/* move it to the front of LRU. */
 		list_move(&e->list, &lc->lru);
 		lc->used--;
 		clear_bit(__LC_STARVING, &lc->flags);
 		smp_mb__after_clear_bit();
 	}
 	RETURN(e->refcnt);
 }

 /**
  * lc_element_by_index
  * @lc: the lru cache to operate on
  * @i: the index of the element to return
  */
 struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
 {
 	BUG_ON(i >= lc->nr_elements);
 	BUG_ON(lc->lc_element[i] == NULL);
 	BUG_ON(lc->lc_element[i]->lc_index != i);
 	return lc->lc_element[i];
 }

 /**
  * lc_index_of
  * @lc: the lru cache to operate on
  * @e: the element to query for its index position in lc->element
  */
 unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
 {
 	PARANOIA_LC_ELEMENT(lc, e);
 	return e->lc_index;
 }

 /**
  * lc_set - associate index with label
  * @lc: the lru cache to operate on
  * @enr: the label to set
  * @index: the element index to associate label with.
  *
  * Used to initialize the active set to some previously recorded state.
  */
 void lc_set(struct lru_cache *lc, unsigned int enr, int index)
 {
 	struct lc_element *e;

 	if (index < 0 || index >= lc->nr_elements)
 		return;

 	e = lc_element_by_index(lc, index);
 	e->lc_number = enr;

 	hlist_del_init(&e->colision);
 	hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
 	list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru);
 }

 /**
  * lc_dump - Dump a complete LRU cache to seq in textual form.
  * @lc: the lru cache to operate on
  * @seq: the &struct seq_file pointer to seq_printf into
  * @utext: user supplied "heading" or other info
  * @detail: function pointer the user may provide to dump further details
  * of the object the lc_element is embedded in.
  */
 void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
 	     void (*detail) (struct seq_file *, struct lc_element *))
 {
 	unsigned int nr_elements = lc->nr_elements;
 	struct lc_element *e;
 	int i;

 	seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext);
 	for (i = 0; i < nr_elements; i++) {
 		e = lc_element_by_index(lc, i);
 		if (e->lc_number == LC_FREE) {
 			seq_printf(seq, "\t%2d: FREE\n", i);
 		} else {
 			seq_printf(seq, "\t%2d: %4u %4u    ", i,
 				   e->lc_number, e->refcnt);
 			detail(seq, e);
 		}
 	}
 }

 EXPORT_SYMBOL(lc_create);
 EXPORT_SYMBOL(lc_reset);
 EXPORT_SYMBOL(lc_destroy);
 EXPORT_SYMBOL(lc_set);
 EXPORT_SYMBOL(lc_del);
 EXPORT_SYMBOL(lc_try_get);
 EXPORT_SYMBOL(lc_find);
 EXPORT_SYMBOL(lc_get);
 EXPORT_SYMBOL(lc_put);
 EXPORT_SYMBOL(lc_changed);
 EXPORT_SYMBOL(lc_element_by_index);
 EXPORT_SYMBOL(lc_index_of);
 EXPORT_SYMBOL(lc_seq_printf_stats);
 EXPORT_SYMBOL(lc_seq_dump_details);
	/*
	lru_cache.c

	This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

	Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
	Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
	Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.

	drbd is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2, or (at your option)
	any later version.

	drbd is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with drbd; see the file COPYING. If not, write to
	the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

	*/

	#include <linux/module.h>
	#include <linux/bitops.h>
	#include <linux/slab.h>
	#include <linux/string.h> /* for memset */
	#include <linux/seq_file.h> /* for seq_printf */
	#include <linux/lru_cache.h>

	MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
	"Lars Ellenberg <lars@linbit.com>");
	MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
	MODULE_LICENSE("GPL");

	/* this is developers aid only.
	* it catches concurrent access (lack of locking on the users part) */
	#define PARANOIA_ENTRY() do { \
	BUG_ON(!lc); \
	BUG_ON(!lc->nr_elements); \
	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
	} while (0)

	#define RETURN(x...) do { \
	clear_bit(__LC_PARANOIA, &lc->flags); \
	smp_mb__after_clear_bit(); return x ; } while (0)

	/* BUG() if e is not one of the elements tracked by lc */
	#define PARANOIA_LC_ELEMENT(lc, e) do { \
	struct lru_cache *lc_ = (lc); \
	struct lc_element *e_ = (e); \
	unsigned i = e_->lc_index; \
	BUG_ON(i >= lc_->nr_elements); \
	BUG_ON(lc_->lc_element[i] != e_); } while (0)

	/**
	* lc_create - prepares to track objects in an active set
	* @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
	* @e_count: number of elements allowed to be active simultaneously
	* @e_size: size of the tracked objects
	* @e_off: offset to the &struct lc_element member in a tracked object
	*
	* Returns a pointer to a newly initialized struct lru_cache on success,
	* or NULL on (allocation) failure.
	*/
	struct lru_cache lc_create(const char name, struct kmem_cache *cache,
	unsigned e_count, size_t e_size, size_t e_off)
	{
	struct hlist_head *slot = NULL;
	struct lc_element **element = NULL;
	struct lru_cache *lc;
	struct lc_element *e;
	unsigned cache_obj_size = kmem_cache_size(cache);
	unsigned i;

	WARN_ON(cache_obj_size < e_size);
	if (cache_obj_size < e_size)
	return NULL;

	/* e_count too big; would probably fail the allocation below anyways.
	* for typical use cases, e_count should be few thousand at most. */
	if (e_count > LC_MAX_ACTIVE)
	return NULL;

	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
	if (!slot)
	goto out_fail;
	element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
	if (!element)
	goto out_fail;

	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
	if (!lc)
	goto out_fail;

	INIT_LIST_HEAD(&lc->in_use);
	INIT_LIST_HEAD(&lc->lru);
	INIT_LIST_HEAD(&lc->free);

	lc->name = name;
	lc->element_size = e_size;
	lc->element_off = e_off;
	lc->nr_elements = e_count;
	lc->new_number = LC_FREE;
	lc->lc_cache = cache;
	lc->lc_element = element;
	lc->lc_slot = slot;

	/* preallocate all objects */
	for (i = 0; i < e_count; i++) {
	void *p = kmem_cache_alloc(cache, GFP_KERNEL);
	if (!p)
	break;
	memset(p, 0, lc->element_size);
	e = p + e_off;
	e->lc_index = i;
	e->lc_number = LC_FREE;
	list_add(&e->list, &lc->free);
	element[i] = e;
	}
	if (i == e_count)
	return lc;

	/* else: could not allocate all elements, give up */
	for (i--; i; i--) {
	void *p = element[i];
	kmem_cache_free(cache, p - e_off);
	}
	kfree(lc);
	out_fail:
	kfree(element);
	kfree(slot);
	return NULL;
	}

	void lc_free_by_index(struct lru_cache *lc, unsigned i)
	{
	void *p = lc->lc_element[i];
	WARN_ON(!p);
	if (p) {
	p -= lc->element_off;
	kmem_cache_free(lc->lc_cache, p);
	}
	}

	/**
	* lc_destroy - frees memory allocated by lc_create()
	* @lc: the lru cache to destroy
	*/
	void lc_destroy(struct lru_cache *lc)
	{
	unsigned i;
	if (!lc)
	return;
	for (i = 0; i < lc->nr_elements; i++)
	lc_free_by_index(lc, i);
	kfree(lc->lc_element);
	kfree(lc->lc_slot);
	kfree(lc);
	}

	/**
	* lc_reset - does a full reset for @lc and the hash table slots.
	* @lc: the lru cache to operate on
	*
	* It is roughly the equivalent of re-allocating a fresh lru_cache object,
	* basically a short cut to lc_destroy(lc); lc = lc_create(...);
	*/
	void lc_reset(struct lru_cache *lc)
	{
	unsigned i;

	INIT_LIST_HEAD(&lc->in_use);
	INIT_LIST_HEAD(&lc->lru);
	INIT_LIST_HEAD(&lc->free);
	lc->used = 0;
	lc->hits = 0;
	lc->misses = 0;
	lc->starving = 0;
	lc->dirty = 0;
	lc->changed = 0;
	lc->flags = 0;
	lc->changing_element = NULL;
	lc->new_number = LC_FREE;
	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);

	for (i = 0; i < lc->nr_elements; i++) {
	struct lc_element *e = lc->lc_element[i];
	void *p = e;
	p -= lc->element_off;
	memset(p, 0, lc->element_size);
	/* re-init it */
	e->lc_index = i;
	e->lc_number = LC_FREE;
	list_add(&e->list, &lc->free);
	}
	}

	/**
	* lc_seq_printf_stats - print stats about @lc into @seq
	* @seq: the seq_file to print into
	* @lc: the lru cache to print statistics of
	*/
	size_t lc_seq_printf_stats(struct seq_file seq, struct lru_cache lc)
	{
	/* NOTE:
	* total calls to lc_get are
	* (starving + hits + misses)
	* misses include "dirty" count (update from an other thread in
	* progress) and "changed", when this in fact lead to an successful
	* update of the cache.
	*/
	return seq_printf(seq, "\t%s: used:%u/%u "
	"hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n",
	lc->name, lc->used, lc->nr_elements,
	lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed);
	}

	static struct hlist_head lc_hash_slot(struct lru_cache lc, unsigned int enr)
	{
	return lc->lc_slot + (enr % lc->nr_elements);
	}


	/**
	* lc_find - find element by label, if present in the hash table
	* @lc: The lru_cache object
	* @enr: element number
	*
	* Returns the pointer to an element, if the element with the requested
	* "label" or element number is present in the hash table,
	* or NULL if not found. Does not change the refcnt.
	*/
	struct lc_element lc_find(struct lru_cache lc, unsigned int enr)
	{
	struct hlist_node *n;
	struct lc_element *e;

	BUG_ON(!lc);
	BUG_ON(!lc->nr_elements);
	hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) {
	if (e->lc_number == enr)
	return e;
	}
	return NULL;
	}

	/* returned element will be "recycled" immediately */
	static struct lc_element lc_evict(struct lru_cache lc)
	{
	struct list_head *n;
	struct lc_element *e;

	if (list_empty(&lc->lru))
	return NULL;

	n = lc->lru.prev;
	e = list_entry(n, struct lc_element, list);

	PARANOIA_LC_ELEMENT(lc, e);

	list_del(&e->list);
	hlist_del(&e->colision);
	return e;
	}

	/**
	* lc_del - removes an element from the cache
	* @lc: The lru_cache object
	* @e: The element to remove
	*
	* @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
	* sets @e->enr to %LC_FREE.
	*/
	void lc_del(struct lru_cache lc, struct lc_element e)
	{
	PARANOIA_ENTRY();
	PARANOIA_LC_ELEMENT(lc, e);
	BUG_ON(e->refcnt);

	e->lc_number = LC_FREE;
	hlist_del_init(&e->colision);
	list_move(&e->list, &lc->free);
	RETURN();
	}

	static struct lc_element lc_get_unused_element(struct lru_cache lc)
	{
	struct list_head *n;

	if (list_empty(&lc->free))
	return lc_evict(lc);

	n = lc->free.next;
	list_del(n);
	return list_entry(n, struct lc_element, list);
	}

	static int lc_unused_element_available(struct lru_cache *lc)
	{
	if (!list_empty(&lc->free))
	return 1; /* something on the free list */
	if (!list_empty(&lc->lru))
	return 1; /* something to evict */

	return 0;
	}


	/**
	* lc_get - get element by label, maybe change the active set
	* @lc: the lru cache to operate on
	* @enr: the label to look up
	*
	* Finds an element in the cache, increases its usage count,
	* "touches" and returns it.
	*
	* In case the requested number is not present, it needs to be added to the
	* cache. Therefore it is possible that an other element becomes evicted from
	* the cache. In either case, the user is notified so he is able to e.g. keep
	* a persistent log of the cache changes, and therefore the objects in use.
	*
	* Return values:
	* NULL
	* The cache was marked %LC_STARVING,
	* or the requested label was not in the active set
	* and a changing transaction is still pending (@lc was marked %LC_DIRTY).
	* Or no unused or free element could be recycled (@lc will be marked as
	* %LC_STARVING, blocking further lc_get() operations).
	*
	* pointer to the element with the REQUESTED element number.
	* In this case, it can be used right away
	*
	* pointer to an UNUSED element with some different element number,
	* where that different number may also be %LC_FREE.
	*
	* In this case, the cache is marked %LC_DIRTY (blocking further changes),
	* and the returned element pointer is removed from the lru list and
	* hash collision chains. The user now should do whatever housekeeping
	* is necessary.
	* Then he must call lc_changed(lc,element_pointer), to finish
	* the change.
	*
	* NOTE: The user needs to check the lc_number on EACH use, so he recognizes
	* any cache set change.
	*/
	struct lc_element lc_get(struct lru_cache lc, unsigned int enr)
	{
	struct lc_element *e;

	PARANOIA_ENTRY();
	if (lc->flags & LC_STARVING) {
	++lc->starving;
	RETURN(NULL);
	}

	e = lc_find(lc, enr);
	if (e) {
	++lc->hits;
	if (e->refcnt++ == 0)
	lc->used++;
	list_move(&e->list, &lc->in_use); /* Not evictable... */
	RETURN(e);
	}

	++lc->misses;

	/* In case there is nothing available and we can not kick out
	* the LRU element, we have to wait ...
	*/
	if (!lc_unused_element_available(lc)) {
	__set_bit(__LC_STARVING, &lc->flags);
	RETURN(NULL);
	}

	/* it was not present in the active set.
	* we are going to recycle an unused (or even "free") element.
	* user may need to commit a transaction to record that change.
	* we serialize on flags & TF_DIRTY */
	if (test_and_set_bit(__LC_DIRTY, &lc->flags)) {
	++lc->dirty;
	RETURN(NULL);
	}

	e = lc_get_unused_element(lc);
	BUG_ON(!e);

	clear_bit(__LC_STARVING, &lc->flags);
	BUG_ON(++e->refcnt != 1);
	lc->used++;

	lc->changing_element = e;
	lc->new_number = enr;

	RETURN(e);
	}

	/* similar to lc_get,
	* but only gets a new reference on an existing element.
	* you either get the requested element, or NULL.
	* will be consolidated into one function.
	*/
	struct lc_element lc_try_get(struct lru_cache lc, unsigned int enr)
	{
	struct lc_element *e;

	PARANOIA_ENTRY();
	if (lc->flags & LC_STARVING) {
	++lc->starving;
	RETURN(NULL);
	}

	e = lc_find(lc, enr);
	if (e) {
	++lc->hits;
	if (e->refcnt++ == 0)
	lc->used++;
	list_move(&e->list, &lc->in_use); /* Not evictable... */
	}
	RETURN(e);
	}

	/**
	* lc_changed - tell @lc that the change has been recorded
	* @lc: the lru cache to operate on
	* @e: the element pending label change
	*/
	void lc_changed(struct lru_cache lc, struct lc_element e)
	{
	PARANOIA_ENTRY();
	BUG_ON(e != lc->changing_element);
	PARANOIA_LC_ELEMENT(lc, e);
	++lc->changed;
	e->lc_number = lc->new_number;
	list_add(&e->list, &lc->in_use);
	hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number));
	lc->changing_element = NULL;
	lc->new_number = LC_FREE;
	clear_bit(__LC_DIRTY, &lc->flags);
	smp_mb__after_clear_bit();
	RETURN();
	}


	/**
	* lc_put - give up refcnt of @e
	* @lc: the lru cache to operate on
	* @e: the element to put
	*
	* If refcnt reaches zero, the element is moved to the lru list,
	* and a %LC_STARVING (if set) is cleared.
	* Returns the new (post-decrement) refcnt.
	*/
	unsigned int lc_put(struct lru_cache lc, struct lc_element e)
	{
	PARANOIA_ENTRY();
	PARANOIA_LC_ELEMENT(lc, e);
	BUG_ON(e->refcnt == 0);
	BUG_ON(e == lc->changing_element);
	if (--e->refcnt == 0) {
	/* move it to the front of LRU. */
	list_move(&e->list, &lc->lru);
	lc->used--;
	clear_bit(__LC_STARVING, &lc->flags);
	smp_mb__after_clear_bit();
	}
	RETURN(e->refcnt);
	}

	/**
	* lc_element_by_index
	* @lc: the lru cache to operate on
	* @i: the index of the element to return
	*/
	struct lc_element lc_element_by_index(struct lru_cache lc, unsigned i)
	{
	BUG_ON(i >= lc->nr_elements);
	BUG_ON(lc->lc_element[i] == NULL);
	BUG_ON(lc->lc_element[i]->lc_index != i);
	return lc->lc_element[i];
	}

	/**
	* lc_index_of
	* @lc: the lru cache to operate on
	* @e: the element to query for its index position in lc->element
	*/
	unsigned int lc_index_of(struct lru_cache lc, struct lc_element e)
	{
	PARANOIA_LC_ELEMENT(lc, e);
	return e->lc_index;
	}

	/**
	* lc_set - associate index with label
	* @lc: the lru cache to operate on
	* @enr: the label to set
	* @index: the element index to associate label with.
	*
	* Used to initialize the active set to some previously recorded state.
	*/
	void lc_set(struct lru_cache *lc, unsigned int enr, int index)
	{
	struct lc_element *e;

	if (index < 0 \|\| index >= lc->nr_elements)
	return;

	e = lc_element_by_index(lc, index);
	e->lc_number = enr;

	hlist_del_init(&e->colision);
	hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
	list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru);
	}

	/**
	* lc_dump - Dump a complete LRU cache to seq in textual form.
	* @lc: the lru cache to operate on
	* @seq: the &struct seq_file pointer to seq_printf into
	* @utext: user supplied "heading" or other info
	* @detail: function pointer the user may provide to dump further details
	* of the object the lc_element is embedded in.
	*/
	void lc_seq_dump_details(struct seq_file seq, struct lru_cache lc, char *utext,
	void (detail) (struct seq_file , struct lc_element *))
	{
	unsigned int nr_elements = lc->nr_elements;
	struct lc_element *e;
	int i;

	seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext);
	for (i = 0; i < nr_elements; i++) {
	e = lc_element_by_index(lc, i);
	if (e->lc_number == LC_FREE) {
	seq_printf(seq, "\t%2d: FREE\n", i);
	} else {
	seq_printf(seq, "\t%2d: %4u %4u ", i,
	e->lc_number, e->refcnt);
	detail(seq, e);
	}
	}
	}

	EXPORT_SYMBOL(lc_create);
	EXPORT_SYMBOL(lc_reset);
	EXPORT_SYMBOL(lc_destroy);
	EXPORT_SYMBOL(lc_set);
	EXPORT_SYMBOL(lc_del);
	EXPORT_SYMBOL(lc_try_get);
	EXPORT_SYMBOL(lc_find);
	EXPORT_SYMBOL(lc_get);
	EXPORT_SYMBOL(lc_put);
	EXPORT_SYMBOL(lc_changed);
	EXPORT_SYMBOL(lc_element_by_index);
	EXPORT_SYMBOL(lc_index_of);
	EXPORT_SYMBOL(lc_seq_printf_stats);
	EXPORT_SYMBOL(lc_seq_dump_details);