Add atomic_sub_* functions to libspl.

Both the SPL and the ZFS libspl export most of the atomic_* functions,
except atomic_sub_* functions which are only exported by the SPL, not by
libspl. This patch remedies that by implementing atomic_sub_* functions
in libspl.
Add FASTWRITE algorithm for synchronous writes.

Currently, ZIL blocks are spread over vdevs using hint block pointers
managed by the ZIL commit code and passed to metaslab_alloc(). Spreading
log blocks accross vdevs is important for performance: indeed, using
mutliple disks in parallel decreases the ZIL commit latency, which is
the main performance metric for synchronous writes. However, the current
implementation suffers from the following issues:

1) It would be best if the ZIL module was not aware of such low-level
details. They should be handled by the ZIO and metaslab modules;

2) Because the hint block pointer is managed per log, simultaneous
commits from multiple logs might use the same vdevs at the same time,
which is inefficient;

3) Because dmu_write() does not honor the block pointer hint, indirect
writes are not spread.

The naive solution of rotating the metaslab rotor each time a block is
allocated for the ZIL or dmu_sync() doesn't work in practice because the
first ZIL block to be written is actually allocated during the previous
commit. Consequently, when metaslab_alloc() decides the vdev for this
block, it will do so while a bunch of other allocations are happening at
the same time (from dmu_sync() and other ZILs). This means the vdev for
this block is chosen more or less at random. When the next commit
happens, there is a high chance (especially when the number of blocks
per commit is slightly less than the number of the disks) that one disk
will have to write two blocks (with a potential seek) while other disks
are sitting idle, which defeats spreading and increases the commit
latency.

This commit introduces a new concept in the metaslab allocator:
fastwrites. Basically, each top-level vdev maintains a counter
indicating the number of synchronous writes (from dmu_sync() and the
ZIL) which have been allocated but not yet completed. When the metaslab
is called with the FASTWRITE flag, it will choose the vdev with the
least amount of pending synchronous writes. If there are multiple vdevs
with the same value, the first matching vdev (starting from the rotor)
is used. Once metaslab_alloc() has decided which vdev the block is
allocated to, it updates the fastwrite counter for this vdev.

The rationale goes like this: when an allocation is done with
FASTWRITE, it "reserves" the vdev until the data is written. Until then,
all future allocations will naturally avoid this vdev, even after a full
rotation of the rotor. As a result, pending synchronous writes at a
given point in time will be nicely spread over all vdevs. This contrasts
with the previous algorithm, which is based on the implicit assumption
that blocks are written instantaneously after they're allocated.

metaslab_fastwrite_mark() and metaslab_fastwrite_unmark() are used to
manually increase or decrease fastwrite counters, respectively. They
should be used with caution, as there is no per-BP tracking of fastwrite
information, so leaks and "double-unmarks" are possible. There is,
however, an assert in the vdev teardown code which will fire if the
fastwrite counters are not zero when the pool is exported or the vdev
removed. Note that as stated above, marking is also done implictly by
metaslab_alloc().

ZIO also got a new FASTWRITE flag; when it is used, ZIO will pass it to
the metaslab when allocating (assuming ZIO does the allocation, which is
only true in the case of dmu_sync). This flag will also trigger an
unmark when zio_done() fires.

A side-effect of the new algorithm is that when a ZIL stops being used,
its last block can stay in the pending state (allocated but not yet
written) for a long time, polluting the fastwrite counters. To avoid
that, I've implemented a somewhat crude but working solution which
unmarks these pending blocks in zil_sync(), thus guaranteeing that
linguering fastwrites will get pruned at each sync event.

The best performance improvements are observed with pools using a large
number of top-level vdevs and heavy synchronous write workflows
(especially indirect writes and concurrent writes from multiple ZILs).
Real-life testing shows a 200% to 300% performance increase with
indirect writes and various commit sizes.
Use the slog even with logbias=throughput.

In the current code, logbias=throughput implies the following:
 1) All synchronous writes are logged in indirect mode.
 2) The slog is not used.

(1) makes sense because it avoids writing the data twice, which is
obviously a good thing when the user wants maximum pool throughput.

(2), however, is a surprising decision. Considering all writes are
indirect, the log record doesn't contain the actual data, only pointers
to DMU blocks. As a result, log records written in logbias=throughput
mode are quite small, and as such, it doesn't make any sense to write
them to the main pool since slogs are usually optimized for small
synchronous writes.

In fact, the current behavior is actually harmful for performance,
because log blocks and data blocks from dmu_sync() seldom have the same
allocation size and as a result are usually allocated from different
metaslabs. This means that if a spindle has to write both log blocks and
DMU blocks (which is likely to happen under heavy load), it will have to
seek between the two. Allocating the log blocks from the slog pool
instead of the main pool avoids these unnecessary seeks.

This commit makes ZFS use the slog on datasets with logbias=throughput.
Real-life performance testing shows a 50% synchronous write performance
increase with some large commit sizes, and no negative effect in other
cases.
Switch KM_SLEEP to KM_PUSHPAGE

This warning indicates the incorrect use of KM_SLEEP in a call
path which must use KM_PUSHPAGE to avoid deadlocking in direct
reclaim.  See commit b8d06fc for additional details.

  SPL: Fixing allocation for task txg_sync (6093) which
  used GFP flags 0x297bda7c with PF_NOFS set

Signed-off-by: Chris Dunlop <chris@onthe.net.au>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1002
Illumos #1950: ztest backwards compatibility testing option.

illumos/illumos-gate@420dfc9585ff67e83ee7800a7ad2ebe1a9145983
Illumos changeset: 13571:a5771a96228c

1950 ztest backwards compatibility testing option

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Eric Schrock <eric.schrock@delphix.com>

Ported-by: Etienne Dechamps <etienne.dechamps@ovh.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Fix mmap() usage in ztest.

illumos/illumos-gate@ad135b5d644628e791c3188a6ecbd9c257961ef8
Illumos changeset: 13700:2889e2596bd6

Note that this is only a partial port of the aforementioned Illumos
changeset.

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <gwilson@delphix.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Reviewed by: Dan Kruchinin <dan.kruchinin@gmail.com>
Approved by: Eric Schrock <Eric.Schrock@delphix.com>

Ported to zfsonlinux by: Etienne Dechamps <etienne.dechamps@ovh.net>
Use dynamic file descriptor numbers in ztest.

Currently, ztest expects to get 3 and 4 as the file descriptors for
data and random files, respectively. This is quite fragile and breaks
easily if ztest is run with these file descriptors already opened
(e.g. in a complex shell script).

This patch fixes the issue by removing the assumptions on the file
descriptor numbers that open() returns.

For the random file (/dev/urandom), the new code doesn't rely on a
shared file descriptor; instead, it reopens the file in the child.

For the data file, the new code writes the file descriptor number into
a "ZTEST_FD_DATA" environment variable so that it can be recovered
after the execv() call.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Minimize ztest stack frame size

To ensure ztest behaves as similarly as possible to the kernel
implementation of ZFS we attempt to honor the kernel stack limits.
This includes keeping the individual stack frame sizes under 1K
in size.  We currently use gcc to detect and enforce this limit.

Therefore to get this building cleanly with full debugging enabled
the stack usage in the following functions has been reduced by
moving the buffer to the heap.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Replace tempnam() with mkstemp()

The use of tempnam() is racy and it should be avoided in favor of
mkstemp().  According to the Linux tempnam(3) man page.

  "Although tempnam() generates names that are difficult to guess,
  it is nevertheless possible that between the time that tempnam()
  returns a pathname, and the time that the program opens it, another
  program might create that pathname using open(2), or create it as
  a symbolic link.  This can lead to security holes.  To avoid such
  possibilities, use the open(2) O_EXCL flag to open the  pathname.
  Or better yet, use mkstemp(3) or tmpfile(3)."

This issue was flagged by gcc.

  ztest.o: In function `setup_data_fd': cmd/ztest/ztest.c:5822:
  warning: the use of `tempnam' is dangerous, better use `mkstemp'

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Verify the return value for warn_unused_result functions

Under Linux the following functions are flagged with the
attribute warn_unused_result, this triggers a warning when
ever they are used without checking the return value.

To handle this case we check the result VERIFY().  It's
better to detect this immediately on failure rather than
segfault farther down in the function.

  ../../cmd/ztest/ztest.c:6033:2: warning:
  ignoring return value of 'asprintf', declared with
  attribute warn_unused_result [-Wunused-result]
  ../../cmd/ztest/ztest.c:739:3: warning:
  ignoring return value of 'realpath', declared with
  attribute warn_unused_result [-Wunused-result]

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Realpath arg 2 must be a minimum of PATH_MAX

The realpath(3) function expects that when a buffer is passed
for the 'resolved_path' that it be at least PATH_MAX in length.
If it's not a buffer overflow may occur.

Therefore the passed buffer size is changed from MAXNAMELEN to
MAXPATHLEN.  We also take this opertunity to dynamically allocate
the buffer to keep it off the stack.

  warning: call to '__realpath_chk_warn' declared with attribute
  warning: second argument of realpath must be either NULL or at
  least PATH_MAX bytes long buffer [enabled by default]

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Align DISCARD requests on zvols.

Currently, when processing DISCARD requests, zvol_discard() calls
dmu_free_long_range() with the precise offset and size of the request.

Unfortunately, this is not optimal for requests that are not aligned to
the zvol block boundaries. Indeed, in the case of an unaligned range,
dnode_free_range() will zero out the unaligned parts. Not only is this
useless since we are not freeing any space by doing so, it is also slow
because it translates to a read-modify-write operation.

This patch fixes the issue by rounding up the discard start offset to
the next volume block boundary, and rounding down the discard end
offset to the previous volume block boundary.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1010
Make sure free ZIO sizes are correct for gang blocks.

Currently, the PSIZE of the block pointer is used as the I/O size for
all free ZIOs. This is incorrect for gang header blocks, for which
PSIZE is the logical size of the gang block data.

This patch fixes the issue by using SPA_GANGBLOCKSIZE as the I/O size
for "free gang header block" ZIOs.
Export avl_is_empty from zavl.

Currently, zavl users cannot call avl_is_empty since it is not
exported. This patch fixes that.
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.

NOTE: this patch only adds the core infrastucture for TRIM. It doesn't
implement actual discard requests on vdevs. In other words, the patch
in itself doesn't actually do anything (yet).

NOTE: you need DKIOCTRIM support in SPL for this patch to build.

Signed-off-by: Etienne Dechamps <etienne.dechamps@ovh.net>
Fix frame size for trim_map_free_locked().

Currently, compilation fails because trim_map_free_locked() exceeds the
frame size. This is because we're allocating a large structure (zio_t)
on the stack.

This patch fixes the issue by only allocating the fields we need from
the zio structure.
Add ZIO TRIM statistics.

This patch adds a new kstat page: zio_trim, which indicates the total
number of bytes TRIMmed, and the number of successful, unsupported and
failed TRIM requests. This makes it easy to verify if TRIM is actually
working or not.
Don't test for gang blocks when populating the trim map.

Since 2fd4ce81a6748b46728127212a1ba384c008696f, gang block free zios
have correct size, so there's no need to skip them. Besides, the test
fails with a NULL dereference bug on RAID-Z because io_bp is NULL in
this case.
Don't TRIM after the SPA has been frozen.

Currently, the TRIM module doesn't check for spa_freeze_txg when
issuing TRIM requests. In a normal run this isn't an issue since
vdev_config_sync() doesn't wake the TRIM thread if the SPA is frozen.

However, when closing a frozen pool, trim_thread_destroy() gets called,
which wakes the TRIM thread, which results in a TRIM commit. As a
result, all TXGs until spa_syncing_txg - txg_limit get TRIMmed, which
includes spa_freeze_txg.

As a result, when reopening, ZFS tries to read data from the frozen
TXG, and fails.

This patch fixes the issue by taking spa_freeze_txg into account when
commiting TRIMs.
Add TRIM support for disk vdevs using Linux DISCARD interface.

This adds DISCARD support to vdev_disk_physio(), and uses it to execute
DKIOCTRIM requests. The implementation is inspired by the Linux
blkdev_issue_discard() function.