crush: generalize descend_once

The legacy behavior is to make the normal number of tries for the
recursive chooseleaf call.  The descend_once tunable changed this to
making a single try and bail if we get a reject (note that it is
impossible to collide in the recursive case).

The new set_chooseleaf_tries lets you select the number of recursive
chooseleaf attempts for indep mode, or default to 1.  Use the same
behavior for firstn, except default to total_tries when the legacy
tunables are set (for compatibility).  This makes the rule step
override the (new) default of 1 recursive attempt, keeping behavior
consistent with indep mode.

Reflects ceph.git commit 685c6950ef3df325ef04ce7c986e36ca2514c5f1.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

net/ceph/crush/mapper.c

@@ -291,7 +291,6 @@ static int is_out(const struct crush_map *map,
  * @out: pointer to output vector
  * @outpos: our position in that vector
  * @recurse_to_leaf: true if we want one device under each item of given type
- * @descend_once: true if we should only try one descent before giving up
  * @out2: second output vector for leaf items (if @recurse_to_leaf)
  */
 static int crush_choose_firstn(const struct crush_map *map,
@@ -302,7 +301,7 @@ static int crush_choose_firstn(const struct crush_map *map,
 			       unsigned int attempts,
 			       unsigned int recurse_attempts,
 			       int recurse_to_leaf,
-			       int descend_once, int *out2)
+			       int *out2)
 {
 	int rep;
 	unsigned int ftotal, flocal;
@@ -389,7 +388,6 @@ static int crush_choose_firstn(const struct crush_map *map,
 							 out2, outpos,
 							 recurse_attempts, 0,
 							 0,
-							 map->chooseleaf_descend_once,
 							 NULL) <= outpos)
 							/* didn't get leaf */
 							reject = 1;
@@ -414,10 +412,7 @@ static int crush_choose_firstn(const struct crush_map *map,
 					ftotal++;
 					flocal++;
 
-					if (reject && descend_once)
-						/* let outer call try again */
-						skip_rep = 1;
-					else if (collide && flocal <= map->choose_local_tries)
+					if (collide && flocal <= map->choose_local_tries)
 						/* retry locally a few times */
 						retry_bucket = 1;
 					else if (map->choose_local_fallback_tries > 0 &&
@@ -639,7 +634,6 @@ int crush_do_rule(const struct crush_map *map,
 	int numrep;
 	int choose_tries = map->choose_total_tries;
 	int choose_leaf_tries = 0;
-	const int descend_once = 0;
 
 	if ((__u32)ruleno >= map->max_rules) {
 		dprintk(" bad ruleno %d\n", ruleno);
@@ -703,6 +697,14 @@ int crush_do_rule(const struct crush_map *map,
 				}
 				j = 0;
 				if (firstn) {
+					int recurse_tries;
+					if (choose_leaf_tries)
+						recurse_tries =
+							choose_leaf_tries;
+					else if (map->chooseleaf_descend_once)
+						recurse_tries = 1;
+					else
+						recurse_tries = choose_tries;
 					osize += crush_choose_firstn(
 						map,
 						map->buckets[-1-w[i]],
@@ -711,9 +713,9 @@ int crush_do_rule(const struct crush_map *map,
 						curstep->arg2,
 						o+osize, j,
 						choose_tries,
-						choose_leaf_tries ? choose_leaf_tries : choose_tries,
+						recurse_tries,
 						recurse_to_leaf,
-						descend_once, c+osize);
+						c+osize);
 				} else {
 					crush_choose_indep(
 						map,
@@ -723,7 +725,8 @@ int crush_do_rule(const struct crush_map *map,
 						curstep->arg2,
 						o+osize, j,
 						choose_tries,
-						choose_leaf_tries ? choose_leaf_tries : 1,
+						choose_leaf_tries ?
+						   choose_leaf_tries : 1,
 						recurse_to_leaf,
 						c+osize,
 						0);