Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Improve TXG handling in the TRIM module.
This patch adds some improvements to the way the trim module considers
TXGs:

- Free ZIOs are registered with the TXG from the ZIO itself, not the
current SPA syncing TXG (which may be out of date);
- L2ARC are registered with a zero TXG number, as L2ARC has no concept
of TXGs;
- The TXG limit for issuing TRIMs is now computed from the last synced
TXG, not the currently syncing TXG. Indeed, under extremely unlikely
race conditions, there is a risk we could trim blocks which have been
freed in a TXG that has not finished syncing, resulting in potential
data corruption in case of a crash.

Reviewed by: pjd (mentor)
Approved by: pjd (mentor)
Obtained from: https://github.com/dechamps/zfs/commit/5b46ad40d9081d75505d6f3bf04ac652445df366
MFC after: 2 weeks

Add TRIM support for L2ARC.

This adds TRIM support to cache vdevs. When ARC buffers are removed
from the L2ARC in arc_hdr_destroy(), arc_release() or l2arc_evict(),
the size previously occupied by the buffer gets scheduled for TRIMming.
As always, actual TRIMs are only issued to the L2ARC after
txg_trim_limit.

Reviewed by: pjd (mentor)
Approved by: pjd (mentor)
Obtained from: https://github.com/dechamps/zfs/commit/31aae373994fd112256607edba7de2359da3e9dc
MFC after: 2 weeks

Add TRIM support.

The code builds a map of regions that were freed. On every write the
code consults the map and eventually removes ranges that were freed
before, but are now overwritten.

Freed blocks are not TRIMed immediately. There is a tunable that defines
how many txg we should wait with TRIMming freed blocks (64 by default).

There is a low priority thread that TRIMs ranges when the time comes.
During TRIM we keep in-flight ranges on a list to detect colliding
writes - we have to delay writes that collide with in-flight TRIMs in
case something will be reordered and write will reached the disk before
the TRIM. We don't have to do the same for in-flight writes, as
colliding writes just remove ranges to TRIM.

Sponsored by: multiplay.co.uk

This work includes some important fixes and some improvements obtained
from the zfsonlinux project, including TRIMming entire vdevs on pool
create/add/attach and on pool import for spare and cache vdevs.

Obtained from: zfsonlinux
Submitted by: Etienne Dechamps <etienne.dechamps@ovh.net>