concurrent small allocation defeats large allocation

Signed-off-by: Paul Dagnelie <pcd@delphix.com>

module/zfs/metaslab.c

@@ -3560,12 +3560,36 @@ metaslab_group_alloc_normal(metaslab_group_t *mg, zio_alloc_list_t *zal,
 			continue;
 		}
 
-		if (metaslab_activate(msp, allocator, activation_weight) != 0) {
+		msp->ms_selected_txg = txg;
+
+		boolean_t activated;
+		int activation_error =
+		    metaslab_activate(msp, allocator, activation_weight);
+		if (activation_error == 0) {
+			activated = B_TRUE;
+		} else if (activation_error == EBUSY ||
+		    activation_error == EEXIST) {
+			/*
+			 * The activation failed because this metaslab was
+			 * concurrently activated by another thread (EBUSY)
+			 * or this allocator concurrently had another
+			 * metaslab activated as primary (EEXIST).  However,
+			 * the metaslab was loaded, so we should continue
+			 * trying to allocate from this metaslab, rather than
+			 * going on to a worse metaslab.
+			 *
+			 * In this case, when we're done with this metaslab,
+			 * we can not passivate it, because it was not
+			 * activated (i.e. is not the active metaslab in the
+			 * mg_primaries array).
+			 */
+			activated = B_FALSE;
+		} else {
+			/* i/o error while loading */
 			mutex_exit(&msp->ms_lock);
 			continue;
 		}
-
-		msp->ms_selected_txg = txg;
+		ASSERT(msp->ms_loaded);
 
 		/*
 		 * Now that we have the lock, recheck to see if we should
@@ -3592,15 +3616,19 @@ metaslab_group_alloc_normal(metaslab_group_t *mg, zio_alloc_list_t *zal,
 		if (msp->ms_condensing) {
 			metaslab_trace_add(zal, mg, msp, asize, d,
 			    TRACE_CONDENSING, allocator);
-			metaslab_passivate(msp, msp->ms_weight &
-			    ~METASLAB_ACTIVE_MASK);
+			if (activated) {
+				metaslab_passivate(msp, msp->ms_weight &
+				    ~METASLAB_ACTIVE_MASK);
+			}
 			mutex_exit(&msp->ms_lock);
 			continue;
 		} else if (msp->ms_disabled > 0) {
 			metaslab_trace_add(zal, mg, msp, asize, d,
 			    TRACE_DISABLED, allocator);
-			metaslab_passivate(msp, msp->ms_weight &
-			    ~METASLAB_ACTIVE_MASK);
+			if (activated) {
+				metaslab_passivate(msp, msp->ms_weight &
+				    ~METASLAB_ACTIVE_MASK);
+			}
 			mutex_exit(&msp->ms_lock);
 			continue;
 		}
@@ -3610,7 +3638,8 @@ metaslab_group_alloc_normal(metaslab_group_t *mg, zio_alloc_list_t *zal,
 
 		if (offset != -1ULL) {
 			/* Proactively passivate the metaslab, if needed */
-			metaslab_segment_may_passivate(msp);
+			if (activated)
+				metaslab_segment_may_passivate(msp);
 			break;
 		}
 next:
@@ -3637,14 +3666,17 @@ metaslab_group_alloc_normal(metaslab_group_t *mg, zio_alloc_list_t *zal,
 		 * currently available for allocation and is accurate
 		 * even within a sync pass.
 		 */
+		uint64_t weight;
 		if (WEIGHT_IS_SPACEBASED(msp->ms_weight)) {
-			uint64_t weight = metaslab_block_maxsize(msp);
+			weight = metaslab_block_maxsize(msp);
 			WEIGHT_SET_SPACEBASED(weight);
-			metaslab_passivate(msp, weight);
 		} else {
-			metaslab_passivate(msp,
-			    metaslab_weight_from_range_tree(msp));
+			weight = metaslab_weight_from_range_tree(msp);
 		}
+		if (activated)
+			metaslab_passivate(msp, weight);
+		else
+			metaslab_group_sort(mg, msp, weight);
 
 		/*
 		 * We have just failed an allocation attempt, check