ceph: CRUSH mapping algorithm
CRUSH is a pseudorandom data distribution function designed to map
inputs onto a dynamic hierarchy of devices, while minimizing the
extent to which inputs are remapped when the devices are added or
removed. It includes some features that are specifically useful for
storage, most notably the ability to map each input onto a set of N
devices that are separated across administrator-defined failure
domains. CRUSH is used to distribute data across the cluster of Ceph
storage nodes.
More information about CRUSH can be found in this paper:
http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/crush/mapper.c b/fs/ceph/crush/mapper.c
new file mode 100644
index 0000000..0f0730c
--- /dev/null
+++ b/fs/ceph/crush/mapper.c
@@ -0,0 +1,589 @@
+
+#ifdef __KERNEL__
+# include <linux/string.h>
+# include <linux/slab.h>
+# include <linux/bug.h>
+# include <linux/kernel.h>
+# ifndef dprintk
+# define dprintk(args...)
+# endif
+#else
+# include <string.h>
+# include <stdio.h>
+# include <stdlib.h>
+# include <assert.h>
+# define BUG_ON(x) assert(!(x))
+# define dprintk(args...) /* printf(args) */
+# define kmalloc(x, f) malloc(x)
+# define kfree(x) free(x)
+#endif
+
+#include "crush.h"
+#include "hash.h"
+
+/*
+ * Implement the core CRUSH mapping algorithm.
+ */
+
+/**
+ * crush_find_rule - find a crush_rule id for a given ruleset, type, and size.
+ * @map: the crush_map
+ * @ruleset: the storage ruleset id (user defined)
+ * @type: storage ruleset type (user defined)
+ * @size: output set size
+ */
+int crush_find_rule(struct crush_map *map, int ruleset, int type, int size)
+{
+ int i;
+
+ for (i = 0; i < map->max_rules; i++) {
+ if (map->rules[i] &&
+ map->rules[i]->mask.ruleset == ruleset &&
+ map->rules[i]->mask.type == type &&
+ map->rules[i]->mask.min_size <= size &&
+ map->rules[i]->mask.max_size >= size)
+ return i;
+ }
+ return -1;
+}
+
+
+/*
+ * bucket choose methods
+ *
+ * For each bucket algorithm, we have a "choose" method that, given a
+ * crush input @x and replica position (usually, position in output set) @r,
+ * will produce an item in the bucket.
+ */
+
+/*
+ * Choose based on a random permutation of the bucket.
+ *
+ * We used to use some prime number arithmetic to do this, but it
+ * wasn't very random, and had some other bad behaviors. Instead, we
+ * calculate an actual random permutation of the bucket members.
+ * Since this is expensive, we optimize for the r=0 case, which
+ * captures the vast majority of calls.
+ */
+static int bucket_perm_choose(struct crush_bucket *bucket,
+ int x, int r)
+{
+ unsigned pr = r % bucket->size;
+ unsigned i, s;
+
+ /* start a new permutation if @x has changed */
+ if (bucket->perm_x != x || bucket->perm_n == 0) {
+ dprintk("bucket %d new x=%d\n", bucket->id, x);
+ bucket->perm_x = x;
+
+ /* optimize common r=0 case */
+ if (pr == 0) {
+ s = crush_hash32_3(x, bucket->id, 0) %
+ bucket->size;
+ bucket->perm[0] = s;
+ bucket->perm_n = 0xffff; /* magic value, see below */
+ goto out;
+ }
+
+ for (i = 0; i < bucket->size; i++)
+ bucket->perm[i] = i;
+ bucket->perm_n = 0;
+ } else if (bucket->perm_n == 0xffff) {
+ /* clean up after the r=0 case above */
+ for (i = 1; i < bucket->size; i++)
+ bucket->perm[i] = i;
+ bucket->perm[bucket->perm[0]] = 0;
+ bucket->perm_n = 1;
+ }
+
+ /* calculate permutation up to pr */
+ for (i = 0; i < bucket->perm_n; i++)
+ dprintk(" perm_choose have %d: %d\n", i, bucket->perm[i]);
+ while (bucket->perm_n <= pr) {
+ unsigned p = bucket->perm_n;
+ /* no point in swapping the final entry */
+ if (p < bucket->size - 1) {
+ i = crush_hash32_3(x, bucket->id, p) %
+ (bucket->size - p);
+ if (i) {
+ unsigned t = bucket->perm[p + i];
+ bucket->perm[p + i] = bucket->perm[p];
+ bucket->perm[p] = t;
+ }
+ dprintk(" perm_choose swap %d with %d\n", p, p+i);
+ }
+ bucket->perm_n++;
+ }
+ for (i = 0; i < bucket->size; i++)
+ dprintk(" perm_choose %d: %d\n", i, bucket->perm[i]);
+
+ s = bucket->perm[pr];
+out:
+ dprintk(" perm_choose %d sz=%d x=%d r=%d (%d) s=%d\n", bucket->id,
+ bucket->size, x, r, pr, s);
+ return bucket->items[s];
+}
+
+/* uniform */
+static int bucket_uniform_choose(struct crush_bucket_uniform *bucket,
+ int x, int r)
+{
+ return bucket_perm_choose(&bucket->h, x, r);
+}
+
+/* list */
+static int bucket_list_choose(struct crush_bucket_list *bucket,
+ int x, int r)
+{
+ int i;
+
+ for (i = bucket->h.size-1; i >= 0; i--) {
+ __u64 w = crush_hash32_4(x, bucket->h.items[i], r,
+ bucket->h.id);
+ w &= 0xffff;
+ dprintk("list_choose i=%d x=%d r=%d item %d weight %x "
+ "sw %x rand %llx",
+ i, x, r, bucket->h.items[i], bucket->item_weights[i],
+ bucket->sum_weights[i], w);
+ w *= bucket->sum_weights[i];
+ w = w >> 16;
+ /*dprintk(" scaled %llx\n", w);*/
+ if (w < bucket->item_weights[i])
+ return bucket->h.items[i];
+ }
+
+ BUG_ON(1);
+ return 0;
+}
+
+
+/* (binary) tree */
+static int height(int n)
+{
+ int h = 0;
+ while ((n & 1) == 0) {
+ h++;
+ n = n >> 1;
+ }
+ return h;
+}
+
+static int left(int x)
+{
+ int h = height(x);
+ return x - (1 << (h-1));
+}
+
+static int right(int x)
+{
+ int h = height(x);
+ return x + (1 << (h-1));
+}
+
+static int terminal(int x)
+{
+ return x & 1;
+}
+
+static int bucket_tree_choose(struct crush_bucket_tree *bucket,
+ int x, int r)
+{
+ int n, l;
+ __u32 w;
+ __u64 t;
+
+ /* start at root */
+ n = bucket->num_nodes >> 1;
+
+ while (!terminal(n)) {
+ /* pick point in [0, w) */
+ w = bucket->node_weights[n];
+ t = (__u64)crush_hash32_4(x, n, r, bucket->h.id) * (__u64)w;
+ t = t >> 32;
+
+ /* descend to the left or right? */
+ l = left(n);
+ if (t < bucket->node_weights[l])
+ n = l;
+ else
+ n = right(n);
+ }
+
+ return bucket->h.items[n >> 1];
+}
+
+
+/* straw */
+
+static int bucket_straw_choose(struct crush_bucket_straw *bucket,
+ int x, int r)
+{
+ int i;
+ int high = 0;
+ __u64 high_draw = 0;
+ __u64 draw;
+
+ for (i = 0; i < bucket->h.size; i++) {
+ draw = crush_hash32_3(x, bucket->h.items[i], r);
+ draw &= 0xffff;
+ draw *= bucket->straws[i];
+ if (i == 0 || draw > high_draw) {
+ high = i;
+ high_draw = draw;
+ }
+ }
+ return bucket->h.items[high];
+}
+
+static int crush_bucket_choose(struct crush_bucket *in, int x, int r)
+{
+ dprintk("choose %d x=%d r=%d\n", in->id, x, r);
+ switch (in->alg) {
+ case CRUSH_BUCKET_UNIFORM:
+ return bucket_uniform_choose((struct crush_bucket_uniform *)in,
+ x, r);
+ case CRUSH_BUCKET_LIST:
+ return bucket_list_choose((struct crush_bucket_list *)in,
+ x, r);
+ case CRUSH_BUCKET_TREE:
+ return bucket_tree_choose((struct crush_bucket_tree *)in,
+ x, r);
+ case CRUSH_BUCKET_STRAW:
+ return bucket_straw_choose((struct crush_bucket_straw *)in,
+ x, r);
+ default:
+ BUG_ON(1);
+/* return in->items[0] */;
+ }
+}
+
+/*
+ * true if device is marked "out" (failed, fully offloaded)
+ * of the cluster
+ */
+static int is_out(struct crush_map *map, __u32 *weight, int item, int x)
+{
+ if (weight[item] >= 0x1000)
+ return 0;
+ if (weight[item] == 0)
+ return 1;
+ if ((crush_hash32_2(x, item) & 0xffff) < weight[item])
+ return 0;
+ return 1;
+}
+
+/**
+ * crush_choose - choose numrep distinct items of given type
+ * @map: the crush_map
+ * @bucket: the bucket we are choose an item from
+ * @x: crush input value
+ * @numrep: the number of items to choose
+ * @type: the type of item to choose
+ * @out: pointer to output vector
+ * @outpos: our position in that vector
+ * @firstn: true if choosing "first n" items, false if choosing "indep"
+ * @recurse_to_leaf: true if we want one device under each item of given type
+ * @out2: second output vector for leaf items (if @recurse_to_leaf)
+ */
+static int crush_choose(struct crush_map *map,
+ struct crush_bucket *bucket,
+ __u32 *weight,
+ int x, int numrep, int type,
+ int *out, int outpos,
+ int firstn, int recurse_to_leaf,
+ int *out2)
+{
+ int rep;
+ int ftotal, flocal;
+ int retry_descent, retry_bucket, skip_rep;
+ struct crush_bucket *in = bucket;
+ int r;
+ int i;
+ int item;
+ int itemtype;
+ int collide, reject;
+ const int orig_tries = 5; /* attempts before we fall back to search */
+ dprintk("choose bucket %d x %d outpos %d\n", bucket->id, x, outpos);
+
+ for (rep = outpos; rep < numrep; rep++) {
+ /* keep trying until we get a non-out, non-colliding item */
+ ftotal = 0;
+ skip_rep = 0;
+ do {
+ retry_descent = 0;
+ in = bucket; /* initial bucket */
+
+ /* choose through intervening buckets */
+ flocal = 0;
+ do {
+ retry_bucket = 0;
+ r = rep;
+ if (in->alg == CRUSH_BUCKET_UNIFORM) {
+ /* be careful */
+ if (firstn || numrep >= in->size)
+ /* r' = r + f_total */
+ r += ftotal;
+ else if (in->size % numrep == 0)
+ /* r'=r+(n+1)*f_local */
+ r += (numrep+1) *
+ (flocal+ftotal);
+ else
+ /* r' = r + n*f_local */
+ r += numrep * (flocal+ftotal);
+ } else {
+ if (firstn)
+ /* r' = r + f_total */
+ r += ftotal;
+ else
+ /* r' = r + n*f_local */
+ r += numrep * (flocal+ftotal);
+ }
+
+ /* bucket choose */
+ if (flocal >= (in->size>>1) &&
+ flocal > orig_tries)
+ item = bucket_perm_choose(in, x, r);
+ else
+ item = crush_bucket_choose(in, x, r);
+ BUG_ON(item >= map->max_devices);
+
+ /* desired type? */
+ if (item < 0)
+ itemtype = map->buckets[-1-item]->type;
+ else
+ itemtype = 0;
+ dprintk(" item %d type %d\n", item, itemtype);
+
+ /* keep going? */
+ if (itemtype != type) {
+ BUG_ON(item >= 0 ||
+ (-1-item) >= map->max_buckets);
+ in = map->buckets[-1-item];
+ continue;
+ }
+
+ /* collision? */
+ collide = 0;
+ for (i = 0; i < outpos; i++) {
+ if (out[i] == item) {
+ collide = 1;
+ break;
+ }
+ }
+
+ if (recurse_to_leaf &&
+ item < 0 &&
+ crush_choose(map, map->buckets[-1-item],
+ weight,
+ x, outpos+1, 0,
+ out2, outpos,
+ firstn, 0, NULL) <= outpos) {
+ reject = 1;
+ } else {
+ /* out? */
+ if (itemtype == 0)
+ reject = is_out(map, weight,
+ item, x);
+ else
+ reject = 0;
+ }
+
+ if (reject || collide) {
+ ftotal++;
+ flocal++;
+
+ if (collide && flocal < 3)
+ /* retry locally a few times */
+ retry_bucket = 1;
+ else if (flocal < in->size + orig_tries)
+ /* exhaustive bucket search */
+ retry_bucket = 1;
+ else if (ftotal < 20)
+ /* then retry descent */
+ retry_descent = 1;
+ else
+ /* else give up */
+ skip_rep = 1;
+ dprintk(" reject %d collide %d "
+ "ftotal %d flocal %d\n",
+ reject, collide, ftotal,
+ flocal);
+ }
+ } while (retry_bucket);
+ } while (retry_descent);
+
+ if (skip_rep) {
+ dprintk("skip rep\n");
+ continue;
+ }
+
+ dprintk("choose got %d\n", item);
+ out[outpos] = item;
+ outpos++;
+ }
+
+ dprintk("choose returns %d\n", outpos);
+ return outpos;
+}
+
+
+/**
+ * crush_do_rule - calculate a mapping with the given input and rule
+ * @map: the crush_map
+ * @ruleno: the rule id
+ * @x: hash input
+ * @result: pointer to result vector
+ * @result_max: maximum result size
+ * @force: force initial replica choice; -1 for none
+ */
+int crush_do_rule(struct crush_map *map,
+ int ruleno, int x, int *result, int result_max,
+ int force, __u32 *weight)
+{
+ int result_len;
+ int force_context[CRUSH_MAX_DEPTH];
+ int force_pos = -1;
+ int a[CRUSH_MAX_SET];
+ int b[CRUSH_MAX_SET];
+ int c[CRUSH_MAX_SET];
+ int recurse_to_leaf;
+ int *w;
+ int wsize = 0;
+ int *o;
+ int osize;
+ int *tmp;
+ struct crush_rule *rule;
+ int step;
+ int i, j;
+ int numrep;
+ int firstn;
+ int rc = -1;
+
+ BUG_ON(ruleno >= map->max_rules);
+
+ rule = map->rules[ruleno];
+ result_len = 0;
+ w = a;
+ o = b;
+
+ /*
+ * determine hierarchical context of force, if any. note
+ * that this may or may not correspond to the specific types
+ * referenced by the crush rule.
+ */
+ if (force >= 0) {
+ if (force >= map->max_devices ||
+ map->device_parents[force] == 0) {
+ /*dprintk("CRUSH: forcefed device dne\n");*/
+ rc = -1; /* force fed device dne */
+ goto out;
+ }
+ if (!is_out(map, weight, force, x)) {
+ while (1) {
+ force_context[++force_pos] = force;
+ if (force >= 0)
+ force = map->device_parents[force];
+ else
+ force = map->bucket_parents[-1-force];
+ if (force == 0)
+ break;
+ }
+ }
+ }
+
+ for (step = 0; step < rule->len; step++) {
+ firstn = 0;
+ switch (rule->steps[step].op) {
+ case CRUSH_RULE_TAKE:
+ w[0] = rule->steps[step].arg1;
+ if (force_pos >= 0) {
+ BUG_ON(force_context[force_pos] != w[0]);
+ force_pos--;
+ }
+ wsize = 1;
+ break;
+
+ case CRUSH_RULE_CHOOSE_LEAF_FIRSTN:
+ case CRUSH_RULE_CHOOSE_FIRSTN:
+ firstn = 1;
+ case CRUSH_RULE_CHOOSE_LEAF_INDEP:
+ case CRUSH_RULE_CHOOSE_INDEP:
+ BUG_ON(wsize == 0);
+
+ recurse_to_leaf =
+ rule->steps[step].op ==
+ CRUSH_RULE_CHOOSE_LEAF_FIRSTN ||
+ rule->steps[step].op ==
+ CRUSH_RULE_CHOOSE_LEAF_INDEP;
+
+ /* reset output */
+ osize = 0;
+
+ for (i = 0; i < wsize; i++) {
+ /*
+ * see CRUSH_N, CRUSH_N_MINUS macros.
+ * basically, numrep <= 0 means relative to
+ * the provided result_max
+ */
+ numrep = rule->steps[step].arg1;
+ if (numrep <= 0) {
+ numrep += result_max;
+ if (numrep <= 0)
+ continue;
+ }
+ j = 0;
+ if (osize == 0 && force_pos >= 0) {
+ /* skip any intermediate types */
+ while (force_pos &&
+ force_context[force_pos] < 0 &&
+ rule->steps[step].arg2 !=
+ map->buckets[-1 -
+ force_context[force_pos]]->type)
+ force_pos--;
+ o[osize] = force_context[force_pos];
+ if (recurse_to_leaf)
+ c[osize] = force_context[0];
+ j++;
+ force_pos--;
+ }
+ osize += crush_choose(map,
+ map->buckets[-1-w[i]],
+ weight,
+ x, numrep,
+ rule->steps[step].arg2,
+ o+osize, j,
+ firstn,
+ recurse_to_leaf, c+osize);
+ }
+
+ if (recurse_to_leaf)
+ /* copy final _leaf_ values to output set */
+ memcpy(o, c, osize*sizeof(*o));
+
+ /* swap t and w arrays */
+ tmp = o;
+ o = w;
+ w = tmp;
+ wsize = osize;
+ break;
+
+
+ case CRUSH_RULE_EMIT:
+ for (i = 0; i < wsize && result_len < result_max; i++) {
+ result[result_len] = w[i];
+ result_len++;
+ }
+ wsize = 0;
+ break;
+
+ default:
+ BUG_ON(1);
+ }
+ }
+ rc = result_len;
+
+out:
+ return rc;
+}
+
+