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, 12 deletions

diff --git a/module/zfs/zfeature.c b/module/zfs/zfeature.c
index 4f4785a0c..cdb9d6dce 100644
--- a/module/zfs/zfeature.c
+++ b/module/zfs/zfeature.c
@@ -369,36 +369,46 @@ spa_feature_enable(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
 	    spa->spa_feat_desc_obj, feature, FEATURE_ACTION_ENABLE, tx));
 }
 
-/*
- * If the specified feature has not yet been enabled, this function returns
- * ENOTSUP; otherwise, this function increments the feature's refcount (or
- * returns EOVERFLOW if the refcount cannot be incremented). This function must
- * be called from syncing context.
- */
 void
 spa_feature_incr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
 {
+	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
 	VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
 	    spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
 	    spa->spa_feat_desc_obj, feature, FEATURE_ACTION_INCR, tx));
 }
 
-/*
- * If the specified feature has not yet been enabled, this function returns
- * ENOTSUP; otherwise, this function decrements the feature's refcount (or
- * returns EOVERFLOW if the refcount is already 0). This function must
- * be called from syncing context.
- */
 void
 spa_feature_decr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
 {
+	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
 	VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
 	    spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
 	    spa->spa_feat_desc_obj, feature, FEATURE_ACTION_DECR, tx));
 }
 
+/*
+ * This interface is for debugging only. Normal consumers should use
+ * spa_feature_is_enabled/spa_feature_is_active.
+ */
+int
+spa_feature_get_refcount(spa_t *spa, zfeature_info_t *feature)
+{
+	int err;
+	uint64_t refcount = 0;
+
+	if (spa_version(spa) < SPA_VERSION_FEATURES)
+		return (B_FALSE);
+
+	err = feature_get_refcount(spa->spa_meta_objset,
+	    spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
+	    feature, &refcount);
+	ASSERT(err == 0 || err == ENOTSUP);
+	return (err == 0 ? refcount : 0);
+}
+
 boolean_t
 spa_feature_is_enabled(spa_t *spa, zfeature_info_t *feature)
 {