Illumos #4101, #4102, #4103, #4105, #4106

4101 metaslab_debug should allow for fine-grained control
4102 space_maps should store more information about themselves
4103 space map object blocksize should be increased
4105 removing a mirrored log device results in a leaked object
4106 asynchronously load metaslab
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Adam Leventhal <[email protected]>
Reviewed by: Sebastien Roy <[email protected]>
Approved by: Garrett D'Amore <[email protected]>

Prior to this patch, space_maps were preferred solely based on the
amount of free space left in each. Unfortunately, this heuristic didn't
contain any information about the make-up of that free space, which
meant we could keep preferring and loading a highly fragmented space map
that wouldn't actually have enough contiguous space to satisfy the
allocation; then unloading that space_map and repeating the process.

This change modifies the space_map's to store additional information
about the contiguous space in the space_map, so that we can use this
information to make a better decision about which space_map to load.
This requires reallocating all space_map objects to increase their
bonus buffer size sizes enough to fit the new metadata.

The above feature can be enabled via a new feature flag introduced by
this change: com.delphix:spacemap_histogram

In addition to the above, this patch allows the space_map block size to
be increase. Currently the block size is set to be 4K in size, which has
certain implications including the following:

    * 4K sector devices will not see any compression benefit
    * large space_maps require more metadata on-disk
    * large space_maps require more time to load (typically random reads)

Now the space_map block size can adjust as needed up to the maximum size
set via the space_map_max_blksz variable.

A bug was fixed which resulted in potentially leaking an object when
removing a mirrored log device. The previous logic for vdev_remove() did
not deal with removing top-level vdevs that are interior vdevs (i.e.
mirror) correctly. The problem would occur when removing a mirrored log
device, and result in the DTL space map object being leaked; because
top-level vdevs don't have DTL space map objects associated with them.

References:
  https://www.illumos.org/issues/4101
  https://www.illumos.org/issues/4102
  https://www.illumos.org/issues/4103
  https://www.illumos.org/issues/4105
  https://www.illumos.org/issues/4106
  https://github.com/illumos/illumos-gate/commit/0713e23

Porting notes:

A handful of kmem_alloc() calls were converted to kmem_zalloc(). Also,
the KM_PUSHPAGE and TQ_PUSHPAGE flags were used as necessary.

Ported-by: Tim Chase <[email protected]>
Signed-off-by: Prakash Surya <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2488

1 files changed, 22 insertions, 2 deletions

diff --git a/man/man5/zpool-features.5 b/man/man5/zpool-features.5
index 243fc769f..57d6120bf 100644
--- a/man/man5/zpool-features.5
+++ b/man/man5/zpool-features.5
@@ -1,5 +1,5 @@
 '\" te
-.\" Copyright (c) 2012 by Delphix. All rights reserved.
+.\" Copyright (c) 2013 by Delphix. All rights reserved.
 .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
 .\" The contents of this file are subject to the terms of the Common Development
 .\" and Distribution License (the "License").  You may not use this file except
@@ -13,7 +13,7 @@
 .\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
 .\" own identifying information:
 .\" Portions Copyright [yyyy] [name of copyright owner]
-.TH ZPOOL-FEATURES 5 "Feb 4, 2013"
+.TH ZPOOL-FEATURES 5 "Aug 27, 2013"
 .SH NAME
 zpool\-features \- ZFS pool feature descriptions
 .SH DESCRIPTION
@@ -228,6 +228,26 @@ read-only compatible, this operation will render the pool unimportable
 on systems without support for the \fBlz4_compress\fR feature. At the
 moment, this operation cannot be reversed. Booting off of
 \fBlz4\fR-compressed root pools is supported.
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBspacemap_histogram\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	com.delphix:spacemap_histogram
+READ\-ONLY COMPATIBLE	yes
+DEPENDENCIES	none
+.TE
+
+This features allows ZFS to maintain more information about how free space
+is organized within the pool. If this feature is \fBenabled\fR, ZFS will
+set this feature to \fBactive\fR when a new space map object is created or
+an existing space map is upgraded to the new format. Once the feature is
+\fBactive\fR, it will remain in that state until the pool is destroyed.
 
 .RE