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, 24 insertions, 0 deletions

diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index 5ed200081..0c45dcf8c 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -182,6 +182,30 @@ Use \fB1\fR for yes (default) and \fB0\fR for no.
 .sp
 .ne 2
 .na
+\fBzfs_metaslab_segment_weight_enabled\fR (int)
+.ad
+.RS 12n
+Enable/disable segment-based metaslab selection.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_metaslab_switch_threshold\fR (int)
+.ad
+.RS 12n
+When using segment-based metaslab selection, continue allocating
+from the active metaslab until \fBlzfs_metaslab_switch_threshold\fR
+worth of buckets have been exhausted.
+.sp
+Default value: \fB2\fR.
+.RE
+
+.sp
+.ne 2
+.na
 \fBmetaslab_debug_load\fR (int)
 .ad
 .RS 12n