Implement soft pressure on UMA cache bucket sizes.

Every time system detects low memory condition decrease bucket sizes for
each zone by one item.  As result, higher memory pressure will push to
smaller bucket sizes and so smaller per-CPU caches and so more efficient
memory use.

Before this change there was no force to oppose buckets growth as result
of practically inevitable zone lock conflicts, and after some run time
per-CPU caches could consume enough RAM to kill the system.
Add two new UMA bucket zones to store 3 and 9 items per bucket.

These new buckets make bucket size self-tuning more soft and precise.
Without them there are buckets for 1, 5, 13, 29, ... items.  While at
bigger sizes difference about 2x is fine, at smallest ones it is 5x and
2.6x respectively.  New buckets make that line look like 1, 3, 5, 9, 13,
29, reducing jumps between steps, making algorithm work softer, allocating
and freeing memory in better fitting chunks.  Otherwise there is quite a
big gap between allocating 128K and 5x128K of RAM at once.
Grow UMA zone bucket size also on lock congestion during item free.

Lock congestion is the same, whether it happens on alloc or free, so
handle it equally.  Now that we have back pressure, there is no problem
to grow buckets a bit faster.  Any way growth is much slower then in 9.x.
Implement mechanism to safely but slowly purge UMA per-CPU caches.

This is a last resort for very low memory condition in case other measures
to free memory were ineffective.  Sequentially cycle through all CPUs and
extract per-CPU cache buckets into zone cache from where they can be freed.
Reenable vfs.zfs.zio.use_uma for amd64, disabled at r209261.

On machines with seveal CPUs and enough RAM this can easily twice improve
ZFS performance or twice reduce CPU usage.  It was disabled three years
ago due to memory and KVA exhaustion reports, but our VM subsystem got
improved a lot since that time, hopefully enough to make another try.
One more BIND remnant: /etc/mtree/BIND.chroot.dist

Discussed with:	des
Support SNI in libfetch

SNI is Server Name Indentification which is a protocol for TLS that
indicates the host that is being connected to at the start of the
handshake. It allows to use Virtual Hosts on HTTPS.

Submitted by:	sbz
Submitted by:	Michael Gmelin <freebsd@grem.de> [1]
PR:		kern/183583 [1]
Reviewed by:	des
Approved by:	bapt
MFC after:	1 week
Follow-up to r258227 and document 'enabled' as a boolean instead of
a string.

Approved by:	bapt
MFC after:	2 days
X-MFC-With:	r258227
Fix build with GCC

SSL_set_tlsext_host_name(3) internally does not modify the host buffer
pased to it. So it is safe to DECONST the struct url* here.

Reported by:	gjb
Approved by:	bapt (implicit)
MFC after:	1 week
X-MFC-With:	r258347
Pull in r191896 from upstream llvm trunk:

  CaptureTracking: Plug a loophole in the "too many uses" heuristic.

  The heuristic was added to avoid spending too much compile time in a
  specially crafted test case (PR17461, PR16474) with many uses on a
  select or bitcast instruction can still trigger the slow case. Add a
  check for that case.

  This only affects compile time, don't have a good way to test it.

This fixes the excessive compile time spent on a specific file of the
graphics/rawtherapee port.

Reported by:	mandree
MFC after:	3 days
fsx: new option to disable msync(MS_SYNC) after each write via mmaped region

This option should be useful for testing if a filesystem uses the
unified buffer / page cache.
Or, if filesystem's emulation of the unified cache works as expected.
This should be the case for e.g. ZFS.

MFC after:	1 week
fsx: add an option to randomly call msync(MS_INVALIDATE)

This call should be a sufficiently close approximation of what happens
when a filesystem is unmounted and remounted.  To be more specific, it
should test that the data that was in the page cache is the same data
that ends up on a stable storage or in a filesystem's internal cache,
if any.
This will catch the cases where a page with modified data is marked as
a clean page for whatever reason.

While there, make logging of the special events (open+close before
plus invalidation now) more generic and slightly better than the previous
hack.

MFC after:	10 days
zfs page_busy: fix the boundaries of the cleared range

This is a fix for a regression introduced in r246293.

vm_page_clear_dirty expects the range to have DEV_BSIZE aligned boundaries,
otherwise it extends them.  Thus it can happen that the whole page is
marked clean while actually having some small dirty region(s).
This commit makes the range properly aligned and ensures that only
the clean data is marked as such.

It would interesting to evaluate how much benefit clearing with DEV_BSIZE
granularity produces.  Perhaps instead we should clear the whole page
when it is completely overwritten and don't bother clearing any bits
if only a portion a page is written.

Reported by:	George Hartzell <hartzell@alerce.com>,
		Richard Todd <rmtodd@servalan.servalan.com>
Tested by:	George Hartzell <hartzell@alerce.com>,
Reviewed by:	kib
MFC after:	5 days
taskqueue_cancel: garbage collect a write-only variable

MFC after:	3 days
"Tim trailing" -> "Trim trailing"
Bugfixes... the host capabilties from FDT data are stored in host.caps, not
host.host_ocr, examine the correct field when setting up the hardware.  Also,
the offset for the capabilties register should be 0x140, not 0x240.

Submitted by:	Ilya Bakulin <ilya@bakulin.de>
Pointy hat to:	me
Add "resize" verb to gmirror(8) and such functionality to geom_mirror(4).
Now it is easy to expand the size of the mirror when all its components
are replaced. Also add g_resize method to geom_mirror class. It will write
updated metadata to new last sector, when parent provider is resized.

Silence from:	geom@
MFC after:	1 month