OpenZFS 7303 - dynamic metaslab selection

This change introduces a new weighting algorithm to improve
metaslab selection. The new weighting algorithm relies on the
SPACEMAP_HISTOGRAM feature. As a result, the metaslab weight
now encodes the type of weighting algorithm used (size-based
vs segment-based).

Porting Notes: The metaslab allocation tracing code is conditionally
removed on linux (dependent on mdb debugger).

Authored by: George Wilson <[email protected]>
Reviewed by: Alex Reece <[email protected]>
Reviewed by: Chris Siden <[email protected]>
Reviewed by: Dan Kimmel <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Paul Dagnelie <[email protected]>
Reviewed by: Pavel Zakharov [email protected]
Reviewed by: Prakash Surya <[email protected]>
Reviewed by: Don Brady <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Ported-by: Don Brady <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/7303
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/d5190931bd
Closes #5404 

1 files changed, 6 insertions, 0 deletions

diff --git a/include/sys/zio.h b/include/sys/zio.h
index 6c5153dcf..1f8708e5a 100644
--- a/include/sys/zio.h
+++ b/include/sys/zio.h
@@ -358,6 +358,11 @@ typedef int zio_pipe_stage_t(zio_t *zio);
 #define	ZIO_REEXECUTE_NOW	0x01
 #define	ZIO_REEXECUTE_SUSPEND	0x02
 
+typedef struct zio_alloc_list {
+	list_t  zal_list;
+	uint64_t zal_size;
+} zio_alloc_list_t;
+
 typedef struct zio_link {
 	zio_t		*zl_parent;
 	zio_t		*zl_child;
@@ -417,6 +422,7 @@ struct zio {
 	avl_node_t	io_queue_node;
 	avl_node_t	io_offset_node;
 	avl_node_t	io_alloc_node;
+	zio_alloc_list_t 	io_alloc_list;
 
 	/* Internal pipeline state */
 	enum zio_flag	io_flags;