Add the rt linux 4.1.3-rt3 as base
[kvmfornfv.git] / kernel / lib / btree.c
diff --git a/kernel/lib/btree.c b/kernel/lib/btree.c
new file mode 100644 (file)
index 0000000..4264871
--- /dev/null
@@ -0,0 +1,801 @@
+/*
+ * lib/btree.c - Simple In-memory B+Tree
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2007-2008 Joern Engel <joern@logfs.org>
+ * Bits and pieces stolen from Peter Zijlstra's code, which is
+ * Copyright 2007, Red Hat Inc. Peter Zijlstra <pzijlstr@redhat.com>
+ * GPLv2
+ *
+ * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
+ *
+ * A relatively simple B+Tree implementation.  I have written it as a learning
+ * exercise to understand how B+Trees work.  Turned out to be useful as well.
+ *
+ * B+Trees can be used similar to Linux radix trees (which don't have anything
+ * in common with textbook radix trees, beware).  Prerequisite for them working
+ * well is that access to a random tree node is much faster than a large number
+ * of operations within each node.
+ *
+ * Disks have fulfilled the prerequisite for a long time.  More recently DRAM
+ * has gained similar properties, as memory access times, when measured in cpu
+ * cycles, have increased.  Cacheline sizes have increased as well, which also
+ * helps B+Trees.
+ *
+ * Compared to radix trees, B+Trees are more efficient when dealing with a
+ * sparsely populated address space.  Between 25% and 50% of the memory is
+ * occupied with valid pointers.  When densely populated, radix trees contain
+ * ~98% pointers - hard to beat.  Very sparse radix trees contain only ~2%
+ * pointers.
+ *
+ * This particular implementation stores pointers identified by a long value.
+ * Storing NULL pointers is illegal, lookup will return NULL when no entry
+ * was found.
+ *
+ * A tricks was used that is not commonly found in textbooks.  The lowest
+ * values are to the right, not to the left.  All used slots within a node
+ * are on the left, all unused slots contain NUL values.  Most operations
+ * simply loop once over all slots and terminate on the first NUL.
+ */
+
+#include <linux/btree.h>
+#include <linux/cache.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#define NODESIZE MAX(L1_CACHE_BYTES, 128)
+
+struct btree_geo {
+       int keylen;
+       int no_pairs;
+       int no_longs;
+};
+
+struct btree_geo btree_geo32 = {
+       .keylen = 1,
+       .no_pairs = NODESIZE / sizeof(long) / 2,
+       .no_longs = NODESIZE / sizeof(long) / 2,
+};
+EXPORT_SYMBOL_GPL(btree_geo32);
+
+#define LONG_PER_U64 (64 / BITS_PER_LONG)
+struct btree_geo btree_geo64 = {
+       .keylen = LONG_PER_U64,
+       .no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64),
+       .no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)),
+};
+EXPORT_SYMBOL_GPL(btree_geo64);
+
+struct btree_geo btree_geo128 = {
+       .keylen = 2 * LONG_PER_U64,
+       .no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64),
+       .no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)),
+};
+EXPORT_SYMBOL_GPL(btree_geo128);
+
+static struct kmem_cache *btree_cachep;
+
+void *btree_alloc(gfp_t gfp_mask, void *pool_data)
+{
+       return kmem_cache_alloc(btree_cachep, gfp_mask);
+}
+EXPORT_SYMBOL_GPL(btree_alloc);
+
+void btree_free(void *element, void *pool_data)
+{
+       kmem_cache_free(btree_cachep, element);
+}
+EXPORT_SYMBOL_GPL(btree_free);
+
+static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp)
+{
+       unsigned long *node;
+
+       node = mempool_alloc(head->mempool, gfp);
+       if (likely(node))
+               memset(node, 0, NODESIZE);
+       return node;
+}
+
+static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n)
+{
+       size_t i;
+
+       for (i = 0; i < n; i++) {
+               if (l1[i] < l2[i])
+                       return -1;
+               if (l1[i] > l2[i])
+                       return 1;
+       }
+       return 0;
+}
+
+static unsigned long *longcpy(unsigned long *dest, const unsigned long *src,
+               size_t n)
+{
+       size_t i;
+
+       for (i = 0; i < n; i++)
+               dest[i] = src[i];
+       return dest;
+}
+
+static unsigned long *longset(unsigned long *s, unsigned long c, size_t n)
+{
+       size_t i;
+
+       for (i = 0; i < n; i++)
+               s[i] = c;
+       return s;
+}
+
+static void dec_key(struct btree_geo *geo, unsigned long *key)
+{
+       unsigned long val;
+       int i;
+
+       for (i = geo->keylen - 1; i >= 0; i--) {
+               val = key[i];
+               key[i] = val - 1;
+               if (val)
+                       break;
+       }
+}
+
+static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n)
+{
+       return &node[n * geo->keylen];
+}
+
+static void *bval(struct btree_geo *geo, unsigned long *node, int n)
+{
+       return (void *)node[geo->no_longs + n];
+}
+
+static void setkey(struct btree_geo *geo, unsigned long *node, int n,
+                  unsigned long *key)
+{
+       longcpy(bkey(geo, node, n), key, geo->keylen);
+}
+
+static void setval(struct btree_geo *geo, unsigned long *node, int n,
+                  void *val)
+{
+       node[geo->no_longs + n] = (unsigned long) val;
+}
+
+static void clearpair(struct btree_geo *geo, unsigned long *node, int n)
+{
+       longset(bkey(geo, node, n), 0, geo->keylen);
+       node[geo->no_longs + n] = 0;
+}
+
+static inline void __btree_init(struct btree_head *head)
+{
+       head->node = NULL;
+       head->height = 0;
+}
+
+void btree_init_mempool(struct btree_head *head, mempool_t *mempool)
+{
+       __btree_init(head);
+       head->mempool = mempool;
+}
+EXPORT_SYMBOL_GPL(btree_init_mempool);
+
+int btree_init(struct btree_head *head)
+{
+       __btree_init(head);
+       head->mempool = mempool_create(0, btree_alloc, btree_free, NULL);
+       if (!head->mempool)
+               return -ENOMEM;
+       return 0;
+}
+EXPORT_SYMBOL_GPL(btree_init);
+
+void btree_destroy(struct btree_head *head)
+{
+       mempool_free(head->node, head->mempool);
+       mempool_destroy(head->mempool);
+       head->mempool = NULL;
+}
+EXPORT_SYMBOL_GPL(btree_destroy);
+
+void *btree_last(struct btree_head *head, struct btree_geo *geo,
+                unsigned long *key)
+{
+       int height = head->height;
+       unsigned long *node = head->node;
+
+       if (height == 0)
+               return NULL;
+
+       for ( ; height > 1; height--)
+               node = bval(geo, node, 0);
+
+       longcpy(key, bkey(geo, node, 0), geo->keylen);
+       return bval(geo, node, 0);
+}
+EXPORT_SYMBOL_GPL(btree_last);
+
+static int keycmp(struct btree_geo *geo, unsigned long *node, int pos,
+                 unsigned long *key)
+{
+       return longcmp(bkey(geo, node, pos), key, geo->keylen);
+}
+
+static int keyzero(struct btree_geo *geo, unsigned long *key)
+{
+       int i;
+
+       for (i = 0; i < geo->keylen; i++)
+               if (key[i])
+                       return 0;
+
+       return 1;
+}
+
+void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key)
+{
+       int i, height = head->height;
+       unsigned long *node = head->node;
+
+       if (height == 0)
+               return NULL;
+
+       for ( ; height > 1; height--) {
+               for (i = 0; i < geo->no_pairs; i++)
+                       if (keycmp(geo, node, i, key) <= 0)
+                               break;
+               if (i == geo->no_pairs)
+                       return NULL;
+               node = bval(geo, node, i);
+               if (!node)
+                       return NULL;
+       }
+
+       if (!node)
+               return NULL;
+
+       for (i = 0; i < geo->no_pairs; i++)
+               if (keycmp(geo, node, i, key) == 0)
+                       return bval(geo, node, i);
+       return NULL;
+}
+EXPORT_SYMBOL_GPL(btree_lookup);
+
+int btree_update(struct btree_head *head, struct btree_geo *geo,
+                unsigned long *key, void *val)
+{
+       int i, height = head->height;
+       unsigned long *node = head->node;
+
+       if (height == 0)
+               return -ENOENT;
+
+       for ( ; height > 1; height--) {
+               for (i = 0; i < geo->no_pairs; i++)
+                       if (keycmp(geo, node, i, key) <= 0)
+                               break;
+               if (i == geo->no_pairs)
+                       return -ENOENT;
+               node = bval(geo, node, i);
+               if (!node)
+                       return -ENOENT;
+       }
+
+       if (!node)
+               return -ENOENT;
+
+       for (i = 0; i < geo->no_pairs; i++)
+               if (keycmp(geo, node, i, key) == 0) {
+                       setval(geo, node, i, val);
+                       return 0;
+               }
+       return -ENOENT;
+}
+EXPORT_SYMBOL_GPL(btree_update);
+
+/*
+ * Usually this function is quite similar to normal lookup.  But the key of
+ * a parent node may be smaller than the smallest key of all its siblings.
+ * In such a case we cannot just return NULL, as we have only proven that no
+ * key smaller than __key, but larger than this parent key exists.
+ * So we set __key to the parent key and retry.  We have to use the smallest
+ * such parent key, which is the last parent key we encountered.
+ */
+void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
+                    unsigned long *__key)
+{
+       int i, height;
+       unsigned long *node, *oldnode;
+       unsigned long *retry_key = NULL, key[geo->keylen];
+
+       if (keyzero(geo, __key))
+               return NULL;
+
+       if (head->height == 0)
+               return NULL;
+       longcpy(key, __key, geo->keylen);
+retry:
+       dec_key(geo, key);
+
+       node = head->node;
+       for (height = head->height ; height > 1; height--) {
+               for (i = 0; i < geo->no_pairs; i++)
+                       if (keycmp(geo, node, i, key) <= 0)
+                               break;
+               if (i == geo->no_pairs)
+                       goto miss;
+               oldnode = node;
+               node = bval(geo, node, i);
+               if (!node)
+                       goto miss;
+               retry_key = bkey(geo, oldnode, i);
+       }
+
+       if (!node)
+               goto miss;
+
+       for (i = 0; i < geo->no_pairs; i++) {
+               if (keycmp(geo, node, i, key) <= 0) {
+                       if (bval(geo, node, i)) {
+                               longcpy(__key, bkey(geo, node, i), geo->keylen);
+                               return bval(geo, node, i);
+                       } else
+                               goto miss;
+               }
+       }
+miss:
+       if (retry_key) {
+               longcpy(key, retry_key, geo->keylen);
+               retry_key = NULL;
+               goto retry;
+       }
+       return NULL;
+}
+EXPORT_SYMBOL_GPL(btree_get_prev);
+
+static int getpos(struct btree_geo *geo, unsigned long *node,
+               unsigned long *key)
+{
+       int i;
+
+       for (i = 0; i < geo->no_pairs; i++) {
+               if (keycmp(geo, node, i, key) <= 0)
+                       break;
+       }
+       return i;
+}
+
+static int getfill(struct btree_geo *geo, unsigned long *node, int start)
+{
+       int i;
+
+       for (i = start; i < geo->no_pairs; i++)
+               if (!bval(geo, node, i))
+                       break;
+       return i;
+}
+
+/*
+ * locate the correct leaf node in the btree
+ */
+static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key, int level)
+{
+       unsigned long *node = head->node;
+       int i, height;
+
+       for (height = head->height; height > level; height--) {
+               for (i = 0; i < geo->no_pairs; i++)
+                       if (keycmp(geo, node, i, key) <= 0)
+                               break;
+
+               if ((i == geo->no_pairs) || !bval(geo, node, i)) {
+                       /* right-most key is too large, update it */
+                       /* FIXME: If the right-most key on higher levels is
+                        * always zero, this wouldn't be necessary. */
+                       i--;
+                       setkey(geo, node, i, key);
+               }
+               BUG_ON(i < 0);
+               node = bval(geo, node, i);
+       }
+       BUG_ON(!node);
+       return node;
+}
+
+static int btree_grow(struct btree_head *head, struct btree_geo *geo,
+                     gfp_t gfp)
+{
+       unsigned long *node;
+       int fill;
+
+       node = btree_node_alloc(head, gfp);
+       if (!node)
+               return -ENOMEM;
+       if (head->node) {
+               fill = getfill(geo, head->node, 0);
+               setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
+               setval(geo, node, 0, head->node);
+       }
+       head->node = node;
+       head->height++;
+       return 0;
+}
+
+static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
+{
+       unsigned long *node;
+       int fill;
+
+       if (head->height <= 1)
+               return;
+
+       node = head->node;
+       fill = getfill(geo, node, 0);
+       BUG_ON(fill > 1);
+       head->node = bval(geo, node, 0);
+       head->height--;
+       mempool_free(node, head->mempool);
+}
+
+static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
+                             unsigned long *key, void *val, int level,
+                             gfp_t gfp)
+{
+       unsigned long *node;
+       int i, pos, fill, err;
+
+       BUG_ON(!val);
+       if (head->height < level) {
+               err = btree_grow(head, geo, gfp);
+               if (err)
+                       return err;
+       }
+
+retry:
+       node = find_level(head, geo, key, level);
+       pos = getpos(geo, node, key);
+       fill = getfill(geo, node, pos);
+       /* two identical keys are not allowed */
+       BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
+
+       if (fill == geo->no_pairs) {
+               /* need to split node */
+               unsigned long *new;
+
+               new = btree_node_alloc(head, gfp);
+               if (!new)
+                       return -ENOMEM;
+               err = btree_insert_level(head, geo,
+                               bkey(geo, node, fill / 2 - 1),
+                               new, level + 1, gfp);
+               if (err) {
+                       mempool_free(new, head->mempool);
+                       return err;
+               }
+               for (i = 0; i < fill / 2; i++) {
+                       setkey(geo, new, i, bkey(geo, node, i));
+                       setval(geo, new, i, bval(geo, node, i));
+                       setkey(geo, node, i, bkey(geo, node, i + fill / 2));
+                       setval(geo, node, i, bval(geo, node, i + fill / 2));
+                       clearpair(geo, node, i + fill / 2);
+               }
+               if (fill & 1) {
+                       setkey(geo, node, i, bkey(geo, node, fill - 1));
+                       setval(geo, node, i, bval(geo, node, fill - 1));
+                       clearpair(geo, node, fill - 1);
+               }
+               goto retry;
+       }
+       BUG_ON(fill >= geo->no_pairs);
+
+       /* shift and insert */
+       for (i = fill; i > pos; i--) {
+               setkey(geo, node, i, bkey(geo, node, i - 1));
+               setval(geo, node, i, bval(geo, node, i - 1));
+       }
+       setkey(geo, node, pos, key);
+       setval(geo, node, pos, val);
+
+       return 0;
+}
+
+int btree_insert(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key, void *val, gfp_t gfp)
+{
+       BUG_ON(!val);
+       return btree_insert_level(head, geo, key, val, 1, gfp);
+}
+EXPORT_SYMBOL_GPL(btree_insert);
+
+static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key, int level);
+static void merge(struct btree_head *head, struct btree_geo *geo, int level,
+               unsigned long *left, int lfill,
+               unsigned long *right, int rfill,
+               unsigned long *parent, int lpos)
+{
+       int i;
+
+       for (i = 0; i < rfill; i++) {
+               /* Move all keys to the left */
+               setkey(geo, left, lfill + i, bkey(geo, right, i));
+               setval(geo, left, lfill + i, bval(geo, right, i));
+       }
+       /* Exchange left and right child in parent */
+       setval(geo, parent, lpos, right);
+       setval(geo, parent, lpos + 1, left);
+       /* Remove left (formerly right) child from parent */
+       btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
+       mempool_free(right, head->mempool);
+}
+
+static void rebalance(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key, int level, unsigned long *child, int fill)
+{
+       unsigned long *parent, *left = NULL, *right = NULL;
+       int i, no_left, no_right;
+
+       if (fill == 0) {
+               /* Because we don't steal entries from a neighbour, this case
+                * can happen.  Parent node contains a single child, this
+                * node, so merging with a sibling never happens.
+                */
+               btree_remove_level(head, geo, key, level + 1);
+               mempool_free(child, head->mempool);
+               return;
+       }
+
+       parent = find_level(head, geo, key, level + 1);
+       i = getpos(geo, parent, key);
+       BUG_ON(bval(geo, parent, i) != child);
+
+       if (i > 0) {
+               left = bval(geo, parent, i - 1);
+               no_left = getfill(geo, left, 0);
+               if (fill + no_left <= geo->no_pairs) {
+                       merge(head, geo, level,
+                                       left, no_left,
+                                       child, fill,
+                                       parent, i - 1);
+                       return;
+               }
+       }
+       if (i + 1 < getfill(geo, parent, i)) {
+               right = bval(geo, parent, i + 1);
+               no_right = getfill(geo, right, 0);
+               if (fill + no_right <= geo->no_pairs) {
+                       merge(head, geo, level,
+                                       child, fill,
+                                       right, no_right,
+                                       parent, i);
+                       return;
+               }
+       }
+       /*
+        * We could also try to steal one entry from the left or right
+        * neighbor.  By not doing so we changed the invariant from
+        * "all nodes are at least half full" to "no two neighboring
+        * nodes can be merged".  Which means that the average fill of
+        * all nodes is still half or better.
+        */
+}
+
+static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key, int level)
+{
+       unsigned long *node;
+       int i, pos, fill;
+       void *ret;
+
+       if (level > head->height) {
+               /* we recursed all the way up */
+               head->height = 0;
+               head->node = NULL;
+               return NULL;
+       }
+
+       node = find_level(head, geo, key, level);
+       pos = getpos(geo, node, key);
+       fill = getfill(geo, node, pos);
+       if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
+               return NULL;
+       ret = bval(geo, node, pos);
+
+       /* remove and shift */
+       for (i = pos; i < fill - 1; i++) {
+               setkey(geo, node, i, bkey(geo, node, i + 1));
+               setval(geo, node, i, bval(geo, node, i + 1));
+       }
+       clearpair(geo, node, fill - 1);
+
+       if (fill - 1 < geo->no_pairs / 2) {
+               if (level < head->height)
+                       rebalance(head, geo, key, level, node, fill - 1);
+               else if (fill - 1 == 1)
+                       btree_shrink(head, geo);
+       }
+
+       return ret;
+}
+
+void *btree_remove(struct btree_head *head, struct btree_geo *geo,
+               unsigned long *key)
+{
+       if (head->height == 0)
+               return NULL;
+
+       return btree_remove_level(head, geo, key, 1);
+}
+EXPORT_SYMBOL_GPL(btree_remove);
+
+int btree_merge(struct btree_head *target, struct btree_head *victim,
+               struct btree_geo *geo, gfp_t gfp)
+{
+       unsigned long key[geo->keylen];
+       unsigned long dup[geo->keylen];
+       void *val;
+       int err;
+
+       BUG_ON(target == victim);
+
+       if (!(target->node)) {
+               /* target is empty, just copy fields over */
+               target->node = victim->node;
+               target->height = victim->height;
+               __btree_init(victim);
+               return 0;
+       }
+
+       /* TODO: This needs some optimizations.  Currently we do three tree
+        * walks to remove a single object from the victim.
+        */
+       for (;;) {
+               if (!btree_last(victim, geo, key))
+                       break;
+               val = btree_lookup(victim, geo, key);
+               err = btree_insert(target, geo, key, val, gfp);
+               if (err)
+                       return err;
+               /* We must make a copy of the key, as the original will get
+                * mangled inside btree_remove. */
+               longcpy(dup, key, geo->keylen);
+               btree_remove(victim, geo, dup);
+       }
+       return 0;
+}
+EXPORT_SYMBOL_GPL(btree_merge);
+
+static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
+                              unsigned long *node, unsigned long opaque,
+                              void (*func)(void *elem, unsigned long opaque,
+                                           unsigned long *key, size_t index,
+                                           void *func2),
+                              void *func2, int reap, int height, size_t count)
+{
+       int i;
+       unsigned long *child;
+
+       for (i = 0; i < geo->no_pairs; i++) {
+               child = bval(geo, node, i);
+               if (!child)
+                       break;
+               if (height > 1)
+                       count = __btree_for_each(head, geo, child, opaque,
+                                       func, func2, reap, height - 1, count);
+               else
+                       func(child, opaque, bkey(geo, node, i), count++,
+                                       func2);
+       }
+       if (reap)
+               mempool_free(node, head->mempool);
+       return count;
+}
+
+static void empty(void *elem, unsigned long opaque, unsigned long *key,
+                 size_t index, void *func2)
+{
+}
+
+void visitorl(void *elem, unsigned long opaque, unsigned long *key,
+             size_t index, void *__func)
+{
+       visitorl_t func = __func;
+
+       func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitorl);
+
+void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
+              size_t index, void *__func)
+{
+       visitor32_t func = __func;
+       u32 *key = (void *)__key;
+
+       func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitor32);
+
+void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
+              size_t index, void *__func)
+{
+       visitor64_t func = __func;
+       u64 *key = (void *)__key;
+
+       func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitor64);
+
+void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
+               size_t index, void *__func)
+{
+       visitor128_t func = __func;
+       u64 *key = (void *)__key;
+
+       func(elem, opaque, key[0], key[1], index);
+}
+EXPORT_SYMBOL_GPL(visitor128);
+
+size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
+                    unsigned long opaque,
+                    void (*func)(void *elem, unsigned long opaque,
+                                 unsigned long *key,
+                                 size_t index, void *func2),
+                    void *func2)
+{
+       size_t count = 0;
+
+       if (!func2)
+               func = empty;
+       if (head->node)
+               count = __btree_for_each(head, geo, head->node, opaque, func,
+                               func2, 0, head->height, 0);
+       return count;
+}
+EXPORT_SYMBOL_GPL(btree_visitor);
+
+size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
+                         unsigned long opaque,
+                         void (*func)(void *elem, unsigned long opaque,
+                                      unsigned long *key,
+                                      size_t index, void *func2),
+                         void *func2)
+{
+       size_t count = 0;
+
+       if (!func2)
+               func = empty;
+       if (head->node)
+               count = __btree_for_each(head, geo, head->node, opaque, func,
+                               func2, 1, head->height, 0);
+       __btree_init(head);
+       return count;
+}
+EXPORT_SYMBOL_GPL(btree_grim_visitor);
+
+static int __init btree_module_init(void)
+{
+       btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
+                       SLAB_HWCACHE_ALIGN, NULL);
+       return 0;
+}
+
+static void __exit btree_module_exit(void)
+{
+       kmem_cache_destroy(btree_cachep);
+}
+
+/* If core code starts using btree, initialization should happen even earlier */
+module_init(btree_module_init);
+module_exit(btree_module_exit);
+
+MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
+MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
+MODULE_LICENSE("GPL");