4873 zvol unmap calls can take a very long time for larger datasets
Reviewed by: George Wilson <george@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Paul Dagnelie <paul.dagnelie@delphix.com>
Reviewed by: Basil Crow <basil.crow@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Approved by: Robert Mustacchi <rm@joyent.com>
5034 ARC's buf_hash_table is too small
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Gordon Ross <gwr@nexenta.com>
	[illumos-gate merge]

commit 63e911b6fce0acc8e2a1d31ebdaf0c4c12580a14
    5034 ARC's buf_hash_table is too small
commit 0f6d88aded0d165f5954688a9b13bac76c38da84
    4873 zvol unmap calls can take a very long time for larger datasets