Adds zpool split to man page

Adds zpool split documentation to the zpool man page.  I only documented
the options that I could get to work.   While it is documented on some
sun blogs that devices can be specified for split, I was not able to get
that to work during my testing.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1456
Don't leak mount flags into kernel

When calling mount(), care must be taken to avoid passing in flags
that are used only by the user space utilities.  Otherwise we may
stomp on flags that are reserved for other purposes in the kernel.

In particular, openSUSE 12.3 kernels have added a new MS_RICHACL
super-block flag whose value conflicts with our MS_COMMENT flag. This
causes incorrect behavior such as the umask being ignored.  The
MS_COMMENT flag essentially serves as a placeholder in the option_map
data structure of zfs_mount.c, but its value is never used. Therefore
we can avoid the conflict by defining it to 0.

The MS_USERS, MS_OWNER, and MS_GROUP flags also conflict with reserved
flags in the kernel. While this is not known to have caused any
problems, it is nevertheless incorrect.  For the purposes of the
mount.zfs helper, the "users", "owner", and "group" options just serve
as hints to set additional implied options.  Therefore we now define
their associated mount flags in terms of the options that they imply
rather than giving them unique values.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1457
Added arcstat.py from FreeNAS

Original source:
  http://support.freenas.org/browser/nanobsd/Files/usr/local/bin/arcstat.py

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1506
Modified arcstat.py to run on linux

* Modified kstat_update() to read arcstats from proc.
* Fix shebang.
* Added Makefile.am entries for arcstat.py

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1506
Improve OpenRC init script

The current zfs OpenRC script's dependencies cause OpenRC to attempt to
unmount ZFS filesystems at shutdown while things were still using them,
which would fail. This is a cosmetic issue, but it should still be
addressed. It probably does not affect systems where the rootfs is a
legacy filesystem, but any system with the rootfs on ZFS needs to run
the ZFS init script after the system is ready to shutdown filesystems.

OpenRC's shutdown process occurs in the reverse order of the startup
process. Therefore running the ZFS shutdown procedure after filesystems
are ready to be unmounted requires running the startup procedure before
fstab. This patch changes the dependencies of the script to expliclty
run before fstab at boot when the rootfs is ZFS and to run after fstab
at boot whenever the rootfs is not ZFS. This should cover most use
cases.

The only cases not covered well by this are systems with legacy
root filesystems where people want to configure fstab to mount a non-ZFS
filesystem off a zvol and possibly also systems whose pools are stored
on network block devices. The former requires that the ZFS script run
before fstab, which could cause ZFS datasets to mount too early and
appear under the fstab mount points. The latter requires that the ZFS
script run after networking starts, which precludes the ability to store
any system information on ZFS. An additional OpenRC script could be
written to handle non-root pools on network block devices, but that will
depend on user demand and developer time.

Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1479
Illumos #3006

3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first
     argument is zero

Reviewed by Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by George Wilson <george.wilson@delphix.com>
Approved by Eric Schrock <eric.schrock@delphix.com>

References:
  illumos/illumos-gate@fb09f5aad449c97fe309678f3f604982b563a96f
  https://illumos.org/issues/3006

Requires:
  zfsonlinux/spl@1c6d149feb4033e4a56fb987004edc5d45288bcb

Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1509
Illumos #3552, #3564

3552 condensing one space map burns 3 seconds of CPU in spa_sync() thread
3564 spa_sync() spends 5-10% of its time in metaslab_sync() (when not condensing)
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  illumos/illumos-gate@16a4a8074274d2d7cc408589cf6359f4a378c861
  https://www.illumos.org/issues/3552
  https://www.illumos.org/issues/3564

Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1513
Fix compile warning on 32-bit systems

The definition of zfs_vdev_holder casts VDEV_HOLDER into a function pointer
passing to linux kernel's block layer function blkdev_get_by_path.
However current VDEV_HOLDER is defined to be wider than 32 bits and the compiler
warns about potential overflows. Instead of specifying different values for 32-bit and
64-bit systems using ifdefs, choose the common factor 32-bit addresses.
Redefine VDEV_HOLDER to 0x2401de7("zholder") here.

Signed-off-by: Ying Zhu <casualfisher@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1520
Illumos #3805 arc shouldn't cache freed blocks

3805 arc shouldn't cache freed blocks
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Richard Elling <richard.elling@dey-sys.com>
Reviewed by: Will Andrews <will@firepipe.net>
Approved by: Dan McDonald <danmcd@nexenta.com>

References:
  illumos/illumos-gate@6e6d5868f52089b9026785bd90257a3d3f6e5ee2
  https://www.illumos.org/issues/3805

ZFS should proactively evict freed blocks from the cache.

On dcenter, we saw that we were caching ~256GB of metadata, while the
pool only had <4GB of metadata on disk.  We were wasting about half the
system's RAM (252GB) on blocks that have been freed.

Even though these freed blocks will never be used again, and thus will
eventually be evicted, this causes us to use memory inefficiently for 2
reasons:

1. A block that is freed has no chance of being accessed again, but will
be kept in memory preferentially to a block that was accessed before it
(and is thus older) but has not been freed and thus has at least some
chance of being accessed again.

2. We partition the ARC into several buckets:
user data that has been accessed only once (MRU)
metadata that has been accessed only once (MRU)
user data that has been accessed more than once (MFU)
metadata that has been accessed more than once (MFU)

The user data vs metadata split is somewhat arbitrary, and the primary
control on how much memory is used to cache data vs metadata is to
simply try to keep the proportion the same as it has been in the past
(each bucket "evicts against" itself).  The secondary control is to
evict data before evicting metadata.

Because of this bucketing, we may end up with one bucket mostly
containing freed blocks that are very old, while another bucket has more
recently accessed, still-allocated blocks.  Data in the useful bucket
(with still-allocated blocks) may be evicted in preference to data in
the useless bucket (with old, freed blocks).

On dcenter, we saw that the MFU metadata bucket was 230MB, while the MFU
data bucket was 27GB and the MRU metadata bucket was 256GB.  However,
the vast majority of data in the MRU metadata bucket (256GB) was freed
blocks, and thus useless.  Meanwhile, the MFU metadata bucket (230MB)
was constantly evicting useful blocks that will be soon needed.

The problem of cache segmentation is a larger problem that needs more
investigation.  However, if we stop caching freed blocks, it should
reduce the impact of this more fundamental issue.

Ported-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1503
Register correct handlers in nvlist_alloc()

The non-blocking allocation handlers in nvlist_alloc() would be
mistakenly assigned if any flags other than KM_SLEEP were passed.
This meant that nvlists allocated with KM_PUSHPUSH or other KM_*
debug flags were effectively always using atomic allocations.

While these failures were unlikely it could lead to assertions
because KM_PUSHPAGE allocations in particular are guaranteed to
succeed or block.  They must never fail.

Since the existing API does not allow us to pass allocation
flags to the private allocators the cleanest thing to do is to
add a KM_PUSHPAGE allocator.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/spl#249