freebsd-nq/module
Matthew Ahrens 9553c533a6 bpobj_enqueue_subobj() should copy small subobj's
When we delete a snapshot, we consolidate some bpobj's together because
we no longer need to keep their entries in separate buckets.  This is
done in constant time by including the "sub" bpobj by reference in the
parent bpobj.

After many snapshots have been deleted, we may have many sub-bpobj's.
Usually, most sub-bpobj's don't contain many BP's.  Compared to this
small payload, the sub-bpobj is relatively heavyweight since it is a
object in the MOS.  A common scenario on a long-lived pool is for the
vast majority of MOS objects to be small sub-bpobj's.

To improve this situation, when consolidating bpobj's together,
bpobj_enqueue_subobj() can copy the contents of small bpobj's into the
parent, and then delete the enqueued bpobj, rather than including it by
reference.  Since this copying is limited in size (to one block), the
consolidation is still constant time, though with a larger constant due
to reading in the one block of the enqueued bpobj.

This idea and mechanism are similar to how we handle "sub-subobj's".
When including a sub-bpobj by reference, if the sub-bpobj itself has
less than a block of sub-sub-bpobj's, the list of sub-sub-bpobj's is
copied to the parent bpobj's list of sub-bpobj's.

Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Paul Zuchowski <pzuchowski@datto.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #8053 
Issue #7908
2018-10-31 11:58:17 -05:00
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avl Update build system and packaging 2018-05-29 16:00:33 -07:00
icp Fedora 28: Fix misc bounds check compiler warnings 2018-08-26 12:55:44 -07:00
lua Update build system and packaging 2018-05-29 16:00:33 -07:00
nvpair Add new fnvlist_lookup_* functions 2018-10-03 15:30:55 -07:00
spl Create /proc/sys/kernel/spl/gitrev with git hash 2018-10-08 21:57:02 -07:00
unicode Update build system and packaging 2018-05-29 16:00:33 -07:00
zcommon Defer new resilvers until the current one ends 2018-10-18 21:06:18 -07:00
zfs bpobj_enqueue_subobj() should copy small subobj's 2018-10-31 11:58:17 -05:00
.gitignore Prepare SPL repo to merge with ZFS repo 2018-05-29 14:51:39 -07:00
Makefile.in Update build system and packaging 2018-05-29 16:00:33 -07:00