--- /dev/null
+/*
+ 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 = kzalloc(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);
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