Use a struct to organize metaslab-group-allocator fields

Each metaslab group (of which there is one per top-level vdev) has
several (4, by default) "metaslab group allocators".  Each "allocator"
has its own metaslab that it prefers to allocate from (the "primary"
allocator), and each can perform allocations concurrently with the other
allocators.  In addition to the primary metaslab, there are several
other fields that need to be tracked separately for each allocator.
These are currently stored as several arrays in the metaslab_group_t,
each array indexed by allocator number.

This change organizes all the metaslab-group-allocator-specific fields
into a new struct, metaslab_group_allocator_t.  The metaslab_group_t now
needs only one array indexed by the allocator number - which contains
the metaslab_group_allocator_t's.

Reviewed-by: Paul Dagnelie <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Matthew Ahrens <[email protected]>
Closes #10213 

1 files changed, 11 insertions, 4 deletions

diff --git a/include/sys/metaslab_impl.h b/include/sys/metaslab_impl.h
index d140f741d..4a7475256 100644
--- a/include/sys/metaslab_impl.h
+++ b/include/sys/metaslab_impl.h
@@ -204,6 +204,16 @@ struct metaslab_class {
 };
 
 /*
+ * Per-allocator data structure.
+ */
+typedef struct metaslab_group_allocator {
+	uint64_t	mga_cur_max_alloc_queue_depth;
+	zfs_refcount_t	mga_alloc_queue_depth;
+	metaslab_t	*mga_primary;
+	metaslab_t	*mga_secondary;
+} metaslab_group_allocator_t;
+
+/*
  * Metaslab groups encapsulate all the allocatable regions (i.e. metaslabs)
  * of a top-level vdev. They are linked together to form a circular linked
  * list and can belong to only one metaslab class. Metaslab groups may become
@@ -214,8 +224,6 @@ struct metaslab_class {
  */
 struct metaslab_group {
 	kmutex_t		mg_lock;
-	metaslab_t		**mg_primaries;
-	metaslab_t		**mg_secondaries;
 	avl_tree_t		mg_metaslab_tree;
 	uint64_t		mg_aliquot;
 	boolean_t		mg_allocatable;		/* can we allocate? */
@@ -263,9 +271,8 @@ struct metaslab_group {
 	 * groups are unable to handle their share of allocations.
 	 */
 	uint64_t		mg_max_alloc_queue_depth;
-	uint64_t		*mg_cur_max_alloc_queue_depth;
-	zfs_refcount_t		*mg_alloc_queue_depth;
 	int			mg_allocators;
+	metaslab_group_allocator_t *mg_allocator; /* array */
 	/*
 	 * A metalab group that can no longer allocate the minimum block
 	 * size will set mg_no_free_space. Once a metaslab group is out