crush: remove mutable part of CRUSH map

Then add it to the working state. It would be very nice if we didn't
have to take a lock to calculate a crush placement. By moving the
permutation array into the working data, we can treat the CRUSH map as
immutable.

Reflects ceph.git commit cbcd039651c0569551cb90d26ce27e1432671f2a.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

6 files changed, 218 insertions, 86 deletions

diff --git a/include/linux/ceph/osdmap.h b/include/linux/ceph/osdmap.h
index 412906609954..cef1cab789b9 100644
--- a/include/linux/ceph/osdmap.h
+++ b/include/linux/ceph/osdmap.h
@@ -175,6 +175,7 @@ struct ceph_osdmap {
 
 	struct mutex crush_scratch_mutex;
 	int crush_scratch_ary[CEPH_PG_MAX_SIZE * 3];
+	void *crush_workspace;
 };
 
 static inline bool ceph_osd_exists(struct ceph_osdmap *map, int osd)
diff --git a/include/linux/crush/crush.h b/include/linux/crush/crush.h
index be8f12b8f195..fbecbd089d75 100644
--- a/include/linux/crush/crush.h
+++ b/include/linux/crush/crush.h
@@ -135,13 +135,6 @@ struct crush_bucket {
 	__u32 size;      /* num items */
 	__s32 *items;
 
-	/*
-	 * cached random permutation: used for uniform bucket and for
-	 * the linear search fallback for the other bucket types.
-	 */
-	__u32 perm_x;  /* @x for which *perm is defined */
-	__u32 perm_n;  /* num elements of *perm that are permuted/defined */
-	__u32 *perm;
 };
 
 struct crush_bucket_uniform {
@@ -211,6 +204,21 @@ struct crush_map {
 	 * device fails. */
 	__u8 chooseleaf_stable;
 
+	/*
+	 * This value is calculated after decode or construction by
+	 * the builder. It is exposed here (rather than having a
+	 * 'build CRUSH working space' function) so that callers can
+	 * reserve a static buffer, allocate space on the stack, or
+	 * otherwise avoid calling into the heap allocator if they
+	 * want to. The size of the working space depends on the map,
+	 * while the size of the scratch vector passed to the mapper
+	 * depends on the size of the desired result set.
+	 *
+	 * Nothing stops the caller from allocating both in one swell
+	 * foop and passing in two points, though.
+	 */
+	size_t working_size;
+
 #ifndef __KERNEL__
 	/*
 	 * version 0 (original) of straw_calc has various flaws.  version 1
@@ -248,4 +256,23 @@ static inline int crush_calc_tree_node(int i)
 	return ((i+1) << 1)-1;
 }
 
+/*
+ * These data structures are private to the CRUSH implementation. They
+ * are exposed in this header file because builder needs their
+ * definitions to calculate the total working size.
+ *
+ * Moving this out of the crush map allow us to treat the CRUSH map as
+ * immutable within the mapper and removes the requirement for a CRUSH
+ * map lock.
+ */
+struct crush_work_bucket {
+	__u32 perm_x; /* @x for which *perm is defined */
+	__u32 perm_n; /* num elements of *perm that are permuted/defined */
+	__u32 *perm;  /* Permutation of the bucket's items */
+};
+
+struct crush_work {
+	struct crush_work_bucket **work; /* Per-bucket working store */
+};
+
 #endif
diff --git a/include/linux/crush/mapper.h b/include/linux/crush/mapper.h
index 5dfd5b1125d2..3303c7fd8a31 100644
--- a/include/linux/crush/mapper.h
+++ b/include/linux/crush/mapper.h
@@ -15,6 +15,8 @@ extern int crush_do_rule(const struct crush_map *map,
 			 int ruleno,
 			 int x, int *result, int result_max,
 			 const __u32 *weights, int weight_max,
-			 int *scratch);
+			 void *cwin, int *scratch);
+
+void crush_init_workspace(const struct crush_map *map, void *v);
 
 #endif
diff --git a/net/ceph/crush/crush.c b/net/ceph/crush/crush.c
index 80d7c3a97cb8..5bf94c04f645 100644
--- a/net/ceph/crush/crush.c
+++ b/net/ceph/crush/crush.c
@@ -45,7 +45,6 @@ int crush_get_bucket_item_weight(const struct crush_bucket *b, int p)
 
 void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b)
 {
-	kfree(b->h.perm);
 	kfree(b->h.items);
 	kfree(b);
 }
@@ -54,14 +53,12 @@ void crush_destroy_bucket_list(struct crush_bucket_list *b)
 {
 	kfree(b->item_weights);
 	kfree(b->sum_weights);
-	kfree(b->h.perm);
 	kfree(b->h.items);
 	kfree(b);
 }
 
 void crush_destroy_bucket_tree(struct crush_bucket_tree *b)
 {
-	kfree(b->h.perm);
 	kfree(b->h.items);
 	kfree(b->node_weights);
 	kfree(b);
@@ -71,7 +68,6 @@ void crush_destroy_bucket_straw(struct crush_bucket_straw *b)
 {
 	kfree(b->straws);
 	kfree(b->item_weights);
-	kfree(b->h.perm);
 	kfree(b->h.items);
 	kfree(b);
 }
@@ -79,7 +75,6 @@ void crush_destroy_bucket_straw(struct crush_bucket_straw *b)
 void crush_destroy_bucket_straw2(struct crush_bucket_straw2 *b)
 {
 	kfree(b->item_weights);
-	kfree(b->h.perm);
 	kfree(b->h.items);
 	kfree(b);
 }
diff --git a/net/ceph/crush/mapper.c b/net/ceph/crush/mapper.c
index 130ab407c5ec..9e75be5ec716 100644
--- a/net/ceph/crush/mapper.c
+++ b/net/ceph/crush/mapper.c
@@ -54,7 +54,6 @@ int crush_find_rule(const struct crush_map *map, int ruleset, int type, int size
 	return -1;
 }
 
-
 /*
  * bucket choose methods
  *
@@ -72,59 +71,60 @@ int crush_find_rule(const struct crush_map *map, int ruleset, int type, int size
  * 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,
+static int bucket_perm_choose(const struct crush_bucket *bucket,
+			      struct crush_work_bucket *work,
 			      int x, int r)
 {
 	unsigned int pr = r % bucket->size;
 	unsigned int i, s;
 
 	/* start a new permutation if @x has changed */
-	if (bucket->perm_x != (__u32)x || bucket->perm_n == 0) {
+	if (work->perm_x != (__u32)x || work->perm_n == 0) {
 		dprintk("bucket %d new x=%d\n", bucket->id, x);
-		bucket->perm_x = x;
+		work->perm_x = x;
 
 		/* optimize common r=0 case */
 		if (pr == 0) {
 			s = crush_hash32_3(bucket->hash, x, bucket->id, 0) %
 				bucket->size;
-			bucket->perm[0] = s;
-			bucket->perm_n = 0xffff;   /* magic value, see below */
+			work->perm[0] = s;
+			work->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) {
+			work->perm[i] = i;
+		work->perm_n = 0;
+	} else if (work->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;
+			work->perm[i] = i;
+		work->perm[work->perm[0]] = 0;
+		work->perm_n = 1;
 	}
 
 	/* calculate permutation up to pr */
-	for (i = 0; i < bucket->perm_n; i++)
+	for (i = 0; i < work->perm_n; i++)
 		dprintk(" perm_choose have %d: %d\n", i, bucket->perm[i]);
-	while (bucket->perm_n <= pr) {
-		unsigned int p = bucket->perm_n;
+	while (work->perm_n <= pr) {
+		unsigned int p = work->perm_n;
 		/* no point in swapping the final entry */
 		if (p < bucket->size - 1) {
 			i = crush_hash32_3(bucket->hash, x, bucket->id, p) %
 				(bucket->size - p);
 			if (i) {
-				unsigned int t = bucket->perm[p + i];
-				bucket->perm[p + i] = bucket->perm[p];
-				bucket->perm[p] = t;
+				unsigned int t = work->perm[p + i];
+				work->perm[p + i] = work->perm[p];
+				work->perm[p] = t;
 			}
 			dprintk(" perm_choose swap %d with %d\n", p, p+i);
 		}
-		bucket->perm_n++;
+		work->perm_n++;
 	}
 	for (i = 0; i < bucket->size; i++)
 		dprintk(" perm_choose  %d: %d\n", i, bucket->perm[i]);
 
-	s = bucket->perm[pr];
+	s = work->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);
@@ -132,14 +132,14 @@ out:
 }
 
 /* uniform */
-static int bucket_uniform_choose(struct crush_bucket_uniform *bucket,
-				 int x, int r)
+static int bucket_uniform_choose(const struct crush_bucket_uniform *bucket,
+				 struct crush_work_bucket *work, int x, int r)
 {
-	return bucket_perm_choose(&bucket->h, x, r);
+	return bucket_perm_choose(&bucket->h, work, x, r);
 }
 
 /* list */
-static int bucket_list_choose(struct crush_bucket_list *bucket,
+static int bucket_list_choose(const struct crush_bucket_list *bucket,
 			      int x, int r)
 {
 	int i;
@@ -155,8 +155,9 @@ static int bucket_list_choose(struct crush_bucket_list *bucket,
 		w *= bucket->sum_weights[i];
 		w = w >> 16;
 		/*dprintk(" scaled %llx\n", w);*/
-		if (w < bucket->item_weights[i])
+		if (w < bucket->item_weights[i]) {
 			return bucket->h.items[i];
+		}
 	}
 
 	dprintk("bad list sums for bucket %d\n", bucket->h.id);
@@ -192,7 +193,7 @@ static int terminal(int x)
 	return x & 1;
 }
 
-static int bucket_tree_choose(struct crush_bucket_tree *bucket,
+static int bucket_tree_choose(const struct crush_bucket_tree *bucket,
 			      int x, int r)
 {
 	int n;
@@ -224,7 +225,7 @@ static int bucket_tree_choose(struct crush_bucket_tree *bucket,
 
 /* straw */
 
-static int bucket_straw_choose(struct crush_bucket_straw *bucket,
+static int bucket_straw_choose(const struct crush_bucket_straw *bucket,
 			       int x, int r)
 {
 	__u32 i;
@@ -301,7 +302,7 @@ static __u64 crush_ln(unsigned int xin)
  *
  */
 
-static int bucket_straw2_choose(struct crush_bucket_straw2 *bucket,
+static int bucket_straw2_choose(const struct crush_bucket_straw2 *bucket,
 				int x, int r)
 {
 	unsigned int i, high = 0;
@@ -344,37 +345,42 @@ static int bucket_straw2_choose(struct crush_bucket_straw2 *bucket,
 			high_draw = draw;
 		}
 	}
+
 	return bucket->h.items[high];
 }
 
 
-static int crush_bucket_choose(struct crush_bucket *in, int x, int r)
+static int crush_bucket_choose(const struct crush_bucket *in,
+			       struct crush_work_bucket *work,
+			       int x, int r)
 {
 	dprintk(" crush_bucket_choose %d x=%d r=%d\n", in->id, x, r);
 	BUG_ON(in->size == 0);
 	switch (in->alg) {
 	case CRUSH_BUCKET_UNIFORM:
-		return bucket_uniform_choose((struct crush_bucket_uniform *)in,
-					  x, r);
+		return bucket_uniform_choose(
+			(const struct crush_bucket_uniform *)in,
+			work, x, r);
 	case CRUSH_BUCKET_LIST:
-		return bucket_list_choose((struct crush_bucket_list *)in,
+		return bucket_list_choose((const struct crush_bucket_list *)in,
 					  x, r);
 	case CRUSH_BUCKET_TREE:
-		return bucket_tree_choose((struct crush_bucket_tree *)in,
+		return bucket_tree_choose((const struct crush_bucket_tree *)in,
 					  x, r);
 	case CRUSH_BUCKET_STRAW:
-		return bucket_straw_choose((struct crush_bucket_straw *)in,
-					   x, r);
+		return bucket_straw_choose(
+			(const struct crush_bucket_straw *)in,
+			x, r);
 	case CRUSH_BUCKET_STRAW2:
-		return bucket_straw2_choose((struct crush_bucket_straw2 *)in,
-					    x, r);
+		return bucket_straw2_choose(
+			(const struct crush_bucket_straw2 *)in,
+			x, r);
 	default:
 		dprintk("unknown bucket %d alg %d\n", in->id, in->alg);
 		return in->items[0];
 	}
 }
 
-
 /*
  * true if device is marked "out" (failed, fully offloaded)
  * of the cluster
@@ -416,7 +422,8 @@ static int is_out(const struct crush_map *map,
  * @parent_r: r value passed from the parent
  */
 static int crush_choose_firstn(const struct crush_map *map,
-			       struct crush_bucket *bucket,
+			       struct crush_work *work,
+			       const struct crush_bucket *bucket,
 			       const __u32 *weight, int weight_max,
 			       int x, int numrep, int type,
 			       int *out, int outpos,
@@ -434,7 +441,7 @@ static int crush_choose_firstn(const struct crush_map *map,
 	int rep;
 	unsigned int ftotal, flocal;
 	int retry_descent, retry_bucket, skip_rep;
-	struct crush_bucket *in = bucket;
+	const struct crush_bucket *in = bucket;
 	int r;
 	int i;
 	int item = 0;
@@ -473,9 +480,13 @@ static int crush_choose_firstn(const struct crush_map *map,
 				if (local_fallback_retries > 0 &&
 				    flocal >= (in->size>>1) &&
 				    flocal > local_fallback_retries)
-					item = bucket_perm_choose(in, x, r);
+					item = bucket_perm_choose(
+						in, work->work[-1-in->id],
+						x, r);
 				else
-					item = crush_bucket_choose(in, x, r);
+					item = crush_bucket_choose(
+						in, work->work[-1-in->id],
+						x, r);
 				if (item >= map->max_devices) {
 					dprintk("   bad item %d\n", item);
 					skip_rep = 1;
@@ -518,19 +529,21 @@ static int crush_choose_firstn(const struct crush_map *map,
 							sub_r = r >> (vary_r-1);
 						else
 							sub_r = 0;
-						if (crush_choose_firstn(map,
-							 map->buckets[-1-item],
-							 weight, weight_max,
-							 x, stable ? 1 : outpos+1, 0,
-							 out2, outpos, count,
-							 recurse_tries, 0,
-							 local_retries,
-							 local_fallback_retries,
-							 0,
-							 vary_r,
-							 stable,
-							 NULL,
-							 sub_r) <= outpos)
+						if (crush_choose_firstn(
+							    map,
+							    work,
+							    map->buckets[-1-item],
+							    weight, weight_max,
+							    x, stable ? 1 : outpos+1, 0,
+							    out2, outpos, count,
+							    recurse_tries, 0,
+							    local_retries,
+							    local_fallback_retries,
+							    0,
+							    vary_r,
+							    stable,
+							    NULL,
+							    sub_r) <= outpos)
 							/* didn't get leaf */
 							reject = 1;
 					} else {
@@ -600,7 +613,8 @@ reject:
  *
  */
 static void crush_choose_indep(const struct crush_map *map,
-			       struct crush_bucket *bucket,
+			       struct crush_work *work,
+			       const struct crush_bucket *bucket,
 			       const __u32 *weight, int weight_max,
 			       int x, int left, int numrep, int type,
 			       int *out, int outpos,
@@ -610,7 +624,7 @@ static void crush_choose_indep(const struct crush_map *map,
 			       int *out2,
 			       int parent_r)
 {
-	struct crush_bucket *in = bucket;
+	const struct crush_bucket *in = bucket;
 	int endpos = outpos + left;
 	int rep;
 	unsigned int ftotal;
@@ -678,7 +692,9 @@ static void crush_choose_indep(const struct crush_map *map,
 					break;
 				}
 
-				item = crush_bucket_choose(in, x, r);
+				item = crush_bucket_choose(
+					in, work->work[-1-in->id],
+					x, r);
 				if (item >= map->max_devices) {
 					dprintk("   bad item %d\n", item);
 					out[rep] = CRUSH_ITEM_NONE;
@@ -724,13 +740,15 @@ static void crush_choose_indep(const struct crush_map *map,
 
 				if (recurse_to_leaf) {
 					if (item < 0) {
-						crush_choose_indep(map,
-						   map->buckets[-1-item],
-						   weight, weight_max,
-						   x, 1, numrep, 0,
-						   out2, rep,
-						   recurse_tries, 0,
-						   0, NULL, r);
+						crush_choose_indep(
+							map,
+							work,
+							map->buckets[-1-item],
+							weight, weight_max,
+							x, 1, numrep, 0,
+							out2, rep,
+							recurse_tries, 0,
+							0, NULL, r);
 						if (out2[rep] == CRUSH_ITEM_NONE) {
 							/* placed nothing; no leaf */
 							break;
@@ -781,6 +799,53 @@ static void crush_choose_indep(const struct crush_map *map,
 #endif
 }
 
+
+/*
+ * This takes a chunk of memory and sets it up to be a shiny new
+ * working area for a CRUSH placement computation. It must be called
+ * on any newly allocated memory before passing it in to
+ * crush_do_rule. It may be used repeatedly after that, so long as the
+ * map has not changed. If the map /has/ changed, you must make sure
+ * the working size is no smaller than what was allocated and re-run
+ * crush_init_workspace.
+ *
+ * If you do retain the working space between calls to crush, make it
+ * thread-local.
+ */
+void crush_init_workspace(const struct crush_map *map, void *v)
+{
+	struct crush_work *w = v;
+	__s32 b;
+
+	/*
+	 * We work by moving through the available space and setting
+	 * values and pointers as we go.
+	 *
+	 * It's a bit like Forth's use of the 'allot' word since we
+	 * set the pointer first and then reserve the space for it to
+	 * point to by incrementing the point.
+	 */
+	v += sizeof(struct crush_work *);
+	w->work = v;
+	v += map->max_buckets * sizeof(struct crush_work_bucket *);
+	for (b = 0; b < map->max_buckets; ++b) {
+		if (!map->buckets[b])
+			continue;
+
+		w->work[b] = v;
+		switch (map->buckets[b]->alg) {
+		default:
+			v += sizeof(struct crush_work_bucket);
+			break;
+		}
+		w->work[b]->perm_x = 0;
+		w->work[b]->perm_n = 0;
+		w->work[b]->perm = v;
+		v += map->buckets[b]->size * sizeof(__u32);
+	}
+	BUG_ON(v - (void *)w != map->working_size);
+}
+
 /**
  * crush_do_rule - calculate a mapping with the given input and rule
  * @map: the crush_map
@@ -790,14 +855,16 @@ static void crush_choose_indep(const struct crush_map *map,
  * @result_max: maximum result size
  * @weight: weight vector (for map leaves)
  * @weight_max: size of weight vector
+ * @cwin: pointer to at least map->working_size bytes of memory
  * @scratch: scratch vector for private use; must be >= 3 * result_max
  */
 int crush_do_rule(const struct crush_map *map,
 		  int ruleno, int x, int *result, int result_max,
 		  const __u32 *weight, int weight_max,
-		  int *scratch)
+		  void *cwin, int *scratch)
 {
 	int result_len;
+	struct crush_work *cw = cwin;
 	int *a = scratch;
 	int *b = scratch + result_max;
 	int *c = scratch + result_max*2;
@@ -807,7 +874,7 @@ int crush_do_rule(const struct crush_map *map,
 	int *o;
 	int osize;
 	int *tmp;
-	struct crush_rule *rule;
+	const struct crush_rule *rule;
 	__u32 step;
 	int i, j;
 	int numrep;
@@ -840,7 +907,7 @@ int crush_do_rule(const struct crush_map *map,
 
 	for (step = 0; step < rule->len; step++) {
 		int firstn = 0;
-		struct crush_rule_step *curstep = &rule->steps[step];
+		const struct crush_rule_step *curstep = &rule->steps[step];
 
 		switch (curstep->op) {
 		case CRUSH_RULE_TAKE:
@@ -936,6 +1003,7 @@ int crush_do_rule(const struct crush_map *map,
 						recurse_tries = choose_tries;
 					osize += crush_choose_firstn(
 						map,
+						cw,
 						map->buckets[bno],
 						weight, weight_max,
 						x, numrep,
@@ -956,6 +1024,7 @@ int crush_do_rule(const struct crush_map *map,
 						    numrep : (result_max-osize));
 					crush_choose_indep(
 						map,
+						cw,
 						map->buckets[bno],
 						weight, weight_max,
 						x, out_size, numrep,
@@ -997,5 +1066,6 @@ int crush_do_rule(const struct crush_map *map,
 			break;
 		}
 	}
+
 	return result_len;
 }
diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index 47df075b31e5..3892e7fa7747 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -153,6 +153,32 @@ bad:
         return -EINVAL;
 }
 
+static void crush_finalize(struct crush_map *c)
+{
+	__s32 b;
+
+	/* Space for the array of pointers to per-bucket workspace */
+	c->working_size = sizeof(struct crush_work) +
+	    c->max_buckets * sizeof(struct crush_work_bucket *);
+
+	for (b = 0; b < c->max_buckets; b++) {
+		if (!c->buckets[b])
+			continue;
+
+		switch (c->buckets[b]->alg) {
+		default:
+			/*
+			 * The base case, permutation variables and
+			 * the pointer to the permutation array.
+			 */
+			c->working_size += sizeof(struct crush_work_bucket);
+			break;
+		}
+		/* Every bucket has a permutation array. */
+		c->working_size += c->buckets[b]->size * sizeof(__u32);
+	}
+}
+
 static struct crush_map *crush_decode(void *pbyval, void *end)
 {
 	struct crush_map *c;
@@ -246,10 +272,6 @@ static struct crush_map *crush_decode(void *pbyval, void *end)
 		b->items = kcalloc(b->size, sizeof(__s32), GFP_NOFS);
 		if (b->items == NULL)
 			goto badmem;
-		b->perm = kcalloc(b->size, sizeof(u32), GFP_NOFS);
-		if (b->perm == NULL)
-			goto badmem;
-		b->perm_n = 0;
 
 		ceph_decode_need(p, end, b->size*sizeof(u32), bad);
 		for (j = 0; j < b->size; j++)
@@ -368,6 +390,8 @@ static struct crush_map *crush_decode(void *pbyval, void *end)
 	dout("crush decode tunable chooseleaf_stable = %d\n",
 	     c->chooseleaf_stable);
 
+	crush_finalize(c);
+
 done:
 	dout("crush_decode success\n");
 	return c;
@@ -753,6 +777,7 @@ void ceph_osdmap_destroy(struct ceph_osdmap *map)
 	kfree(map->osd_weight);
 	kfree(map->osd_addr);
 	kfree(map->osd_primary_affinity);
+	kfree(map->crush_workspace);
 	kfree(map);
 }
 
@@ -810,12 +835,23 @@ static int osdmap_set_max_osd(struct ceph_osdmap *map, int max)
 
 static int osdmap_set_crush(struct ceph_osdmap *map, struct crush_map *crush)
 {
+	void *workspace;
+
 	if (IS_ERR(crush))
 		return PTR_ERR(crush);
 
+	workspace = kmalloc(crush->working_size, GFP_NOIO);
+	if (!workspace) {
+		crush_destroy(crush);
+		return -ENOMEM;
+	}
+	crush_init_workspace(crush, workspace);
+
 	if (map->crush)
 		crush_destroy(map->crush);
+	kfree(map->crush_workspace);
 	map->crush = crush;
+	map->crush_workspace = workspace;
 	return 0;
 }
 
@@ -1940,7 +1976,8 @@ static int do_crush(struct ceph_osdmap *map, int ruleno, int x,
 
 	mutex_lock(&map->crush_scratch_mutex);
 	r = crush_do_rule(map->crush, ruleno, x, result, result_max,
-			  weight, weight_max, map->crush_scratch_ary);
+			  weight, weight_max, map->crush_workspace,
+			  map->crush_scratch_ary);
 	mutex_unlock(&map->crush_scratch_mutex);
 
 	return r;