crush: new SET_CHOOSE_LEAF_TRIES command

Explicitly control the number of sample attempts, and allow the number of
tries in the recursive call to be explicitly controlled via the rule. This
is important because the amount of time we want to spend looking for a
solution may be rule dependent (e.g., higher for the wide indep pool than
the rep pools).

(We should do the same for the other tunables, by the way!)

Reflects ceph.git commit c43c893be872f709c787bc57f46c0e97876ff681.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

include/linux/crush/crush.h

@@ -46,6 +46,8 @@ enum {
 	CRUSH_RULE_EMIT = 4,          /* no args */
 	CRUSH_RULE_CHOOSE_LEAF_FIRSTN = 6,
 	CRUSH_RULE_CHOOSE_LEAF_INDEP = 7,
+
+	CRUSH_RULE_SET_CHOOSE_LEAF_TRIES = 9,
 };
 
 /*

net/ceph/crush/mapper.c

@@ -459,6 +459,8 @@ static void crush_choose_indep(const struct crush_map *map,
 			       const __u32 *weight, int weight_max,
 			       int x, int left, int numrep, int type,
 			       int *out, int outpos,
+			       unsigned int attempts,
+			       unsigned int recurse_attempts,
 			       int recurse_to_leaf,
 			       int *out2,
 			       int parent_r)
@@ -483,7 +485,7 @@ static void crush_choose_indep(const struct crush_map *map,
 			out2[rep] = CRUSH_ITEM_UNDEF;
 	}
 
-	for (ftotal = 0; left > 0 && ftotal < map->choose_total_tries; ftotal++) {
+	for (ftotal = 0; left > 0 && ftotal < attempts; ftotal++) {
 		for (rep = outpos; rep < endpos; rep++) {
 			if (out[rep] != CRUSH_ITEM_UNDEF)
 				continue;
@@ -568,6 +570,7 @@ static void crush_choose_indep(const struct crush_map *map,
 						   weight, weight_max,
 						   x, 1, numrep, 0,
 						   out2, rep,
+						   recurse_attempts, 0,
 						   0, NULL, r);
 						if (out2[rep] == CRUSH_ITEM_NONE) {
 							/* placed nothing; no leaf */
@@ -631,6 +634,7 @@ int crush_do_rule(const struct crush_map *map,
 	__u32 step;
 	int i, j;
 	int numrep;
+	int choose_leaf_tries = 1;
 	const int descend_once = 0;
 
 	if ((__u32)ruleno >= map->max_rules) {
@@ -653,6 +657,11 @@ int crush_do_rule(const struct crush_map *map,
 			wsize = 1;
 			break;
 
+		case CRUSH_RULE_SET_CHOOSE_LEAF_TRIES:
+			if (curstep->arg1 > 0)
+				choose_leaf_tries = curstep->arg1;
+			break;
+
 		case CRUSH_RULE_CHOOSE_LEAF_FIRSTN:
 		case CRUSH_RULE_CHOOSE_FIRSTN:
 			firstn = 1;
@@ -702,6 +711,8 @@ int crush_do_rule(const struct crush_map *map,
 						x, numrep, numrep,
 						curstep->arg2,
 						o+osize, j,
+						map->choose_total_tries,
+						choose_leaf_tries,
 						recurse_to_leaf,
 						c+osize,
 						0);