3 files changed, 565 insertions, 0 deletions

diff --git a/lib/Kconfig b/lib/Kconfig
index bb1326d3839c..1cfe51628e1b 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -200,4 +200,7 @@ config NLATTR
 config GENERIC_ATOMIC64
        bool
 
+config LRU_CACHE
+        tristate
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 2e78277eff9d..347ad8db29d3 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -91,6 +91,8 @@ obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
 
 obj-$(CONFIG_NLATTR) += nlattr.o
 
+obj-$(CONFIG_LRU_CACHE) += lru_cache.o
+
 obj-$(CONFIG_DMA_API_DEBUG) += dma-debug.o
 
 obj-$(CONFIG_GENERIC_CSUM) += checksum.o
diff --git a/lib/lru_cache.c b/lib/lru_cache.c
new file mode 100644
index 000000000000..270de9d31b8c
--- /dev/null
+++ b/lib/lru_cache.c
@@ -0,0 +1,560 @@
+/*
+   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);