Linux kernel 3.17 removes the action function argument from
wait_on_bit(). Add autoconf test and compatibility macro to support
the new interface.
The former "wait_on_bit" interface required an 'action' function to
be provided which does the actual waiting. There were over 20 such
functions in the kernel, many of them identical, though most cases
can be satisfied by one of just two functions: one which uses
io_schedule() and one which just uses schedule(). This API change
was made to consolidate all of those redundant wait functions.
References: torvalds/linux@7431620
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#378
For small objects the Linux slab allocator should be used to make the most
efficient use of the memory. However, large objects are not supported by
the Linux slab and therefore the SPL implementation is preferred. A cutoff
of 16K was determined to be optimal for architectures using 4K pages.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: DHE <git@dehacked.net>
Issue #356Closes#379
Reinstate the correct default behavior of returning the number of objects
in the cache for reclaim. This behavior was disabled in recent releases
to do occasional reports of spinning in shrink_slabs(). Those issues have
been resolved and can no longer can be reproduced. See commit 376dc35.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: DHE <git@dehacked.net>
Issue #358Closes#379
The atomic_swap_32() function maps to atomic_xchg(), and
the atomic_swap_64() function maps to atomic64_xchg().
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#377
Added highbit64() and howmany() which are used in recent upstream
code. Both highbit() and highbit64() should at some point be
re-factored to use the optimized fls() and fls64() functions.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes#363
There have been issues in the past where excessive debug logging
to the console has resulted in significant performance impacts.
In the vast majority of these cases only a few stack traces are
required to diagnose the issue. Therefore, stack traces dumped to
the console will now we limited to 5 every 60s.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Closes#374
Spl's debugging and assertion macros macro used the typical do/while(0)
form for if/else friendliness, however, this limits their use in contexts
where a do loop is not valid; such as within another multi-statement
style macro.
The following macros have been converted to not use do/while(0):
PANIC, ASSERT, ASSERTF, VERIFY, VERIFY3_IMPL
PANIC has been converted to a wrapper around the new spl_PANIC() function.
The other macros have been converted to use the "&&" operator for the
branch-predicition conditional and also to use spl_PANIC().
The __ASSERT() macro was not touched. It is only used by the debugging
infrastructure and that code, including this macro, will be retired when
the tracepoint patches are merged.
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#367
Set LANG=C before calling 'rpmbuild' to avoid rpmbuild failing on
the translated date string in the changelog.
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#306
Running 'yum upgrade spl-dkms' package could appear to work properly
and still leave you with no spl modules installed. This will occur
when only the spl release, and not the version, are incremented.
This may be the case for a fast moving spl-testing repository.
During the upgrade process DKMS will realize that spl-x.y.z is already
installed and remove it. DKMS then correctly builds the new modules
for spl-x.y.z. However, as a final step when the old spl-x.y.z-r is
removed the %preun script runs and removes the newly build modules.
To handle this case the %preun script has been updated to only run
when the installed version exactly matches the full spec file version.
This change also updated ChangeLog section based on the DKMS
reference spec file.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
When creating packages in a git repository the release number
can be automatically set by 'git describe'. This normally works
well but if your repository has newer tags which match the form
NAME-VERSION* the release may be incorrectly calculated. To
prevent this the match patten has been restricted to NAME-VERSION.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
The correct behavior for all registered shrinkers is to return the
number of objects in their cache. In theory this allows the Linux
VM to balance memory reclaim across all registered caches.
In commit b9b3715 this behavior was disabled in favor of returning
-1 which notifies the VM that no additional objects are available
for reclaim. This was done as a workaround to resolve thrashing
in shrink_slabs() which could occur when memory was low and numerous
core where in reclaim. Unfortunately, this has been observed to
increase the likelihood of OOM events when SPL slab consumers are
responsible for consuming the majority of memory.
Therefore, this patch makes this behavior tunable. Setting the
spl_kmem_cache_reclaim module option to 0x1 will result in the
shrinker only being called once. This is the default behavior.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Closes#358
For small objects the Linux slab allocator has several advantages
over its counterpart in the SPL. These include:
1) It is more memory-efficient and packs objects more tightly.
2) It is continually tuned to maximize performance.
Therefore it makes sense to layer the SPLs slab allocator on top
of the Linux slab allocator. This allows us to leverage the
advantages above while preserving the Illumos semantics we depend
on. However, there are some things we need to be careful of:
1) The Linux slab allocator was never designed to work well with
large objects. Because the SPL slab must still handle this use
case a cut off limit was added to transition from Linux slab
backed objects to kmem or vmem backed slabs.
spl_kmem_cache_slab_limit - Objects less than or equal to this
size in bytes will be backed by the Linux slab. By default
this value is zero which disables the Linux slab functionality.
Reasonable values for this cut off limit are in the range of
4096-16386 bytes.
spl_kmem_cache_kmem_limit - Objects less than or equal to this
size in bytes will be backed by a kmem slab. Objects over this
size will be vmem backed instead. This value defaults to
1/8 a page, or 512 bytes on an x86_64 architecture.
2) Be aware that using the Linux slab may inadvertently introduce
new deadlocks. Care has been taken previously to ensure that
all allocations which occur in the write path use GFP_NOIO.
However, there may be internal allocations performed in the
Linux slab which do not honor these flags. If this is the case
a deadlock may occur.
The path forward is definitely to start relying on the Linux slab.
But for that to happen we need to start building confidence that
there aren't any unexpected surprises lurking for us. And ideally
need to move completely away from using the SPLs slab for large
memory allocations. This patch is a first step.
NOTES:
1) The KMC_NOMAGAZINE flag was leveraged to support the Linux slab
backed caches but it is not supported for kmem/vmem backed caches.
2) Regardless of the spl_kmem_cache_*_limit settings a cache may
be explicitly set to a given type by passed the KMC_KMEM,
KMC_VMEM, or KMC_SLAB flags during cache creation.
3) The constructors, destructors, and reclaim callbacks are all
functional and will be called regardless of the cache type.
4) KMC_SLAB caches will not appear in /proc/spl/kmem/slab due to
the issues involved in presenting correct object accounting.
Instead they will appear in /proc/slabinfo under the same names.
5) Several kmem SPLAT tests needed to be fixed because they relied
incorrectly on internal kmem slab accounting. With the updated
test cases all the SPLAT tests pass as expected.
6) An autoconf test was added to ensure that the __GFP_COMP flag
was correctly added to the default flags used when allocating
a slab. This is required to ensure all pages in higher order
slabs are properly refcounted, see ae16ed9.
7) When using the SLUB allocator there is no need to attempt to
set the __GFP_COMP flag. This has been the default behavior
for the SLUB since Linux 2.6.25.
8) When using the SLUB it may be desirable to set the slub_nomerge
kernel parameter to prevent caches from being merged.
Original-patch-by: DHE <git@dehacked.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: DHE <git@dehacked.net>
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Closes#356
Detect the updated vfs_rename() interface and call it with an
extra flags argument.
References:
torvalds/linux@520c8b1
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #355
These macro's were exposed to make them available to other
parts of the kernel and modules.
References:
torvalds/linux@6b6350f
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #355
The problem is described in commit aeeb4e0c0a.
However, instead of disabling the binding to CPU altogether we just keep the
last CPU index across calls to taskq_create() and thus achieve even
distribution of the taskq threads across all available CPUs.
The implementation based on assumption that task queues initialization
performed in serial manner.
Signed-off-by: Andrey Vesnovaty <andrey.vesnovaty@gmail.com>
Signed-off-by: Andrey Vesnovaty <andreyv@infinidat.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#336
When using __get_free_pages to get high order memory, only the first page's
_count will set to 1, other's will be 0. When an internal page get passed into
rbd, it will eventully go into tcp_sendpage. There, it will be called with
get_page and put_page, and get freed erroneously when _count jump back to 0.
The solution to this problem is to use compound page. All pages in a
high order compound page share a single _count. So get_page and put_page in
tcp_sendpage will not cause _count jump to 0.
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#251
Using the ARM reference simulation (fast model foundation v8) I
cross compiled spl and zfs, to confirm it works on ARMv8 (64 bit
arm architecture, called aarch64 in Linux).
As it is based on previous ARM porting, the resulting patch is
disappointingly small, there was very little to do. The code fixes
the compile issues and has light testing done.
Signed-off-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#351
This behavior is more consistent with the way memory reclaim
is expected to work under Linux.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#349
By default maximal number of objects in slab can't exceed (16*2 - 1) and slab
size can't exceed 32M.
Today's high end servers having couple hundreds of RAM available for ARC may
run into a trouble with virtual memory because of the restriction mentioned
above.
Problem:
Reasons for very high number of virtual memory allocations:
* Real slab size very small relative to the size of the entire RAM
* Slabs allocated on virtual memory and fill entire ARC
The result is very high number of allocated virtual memory ranges (hundreds of
ranges). When virtual memory subsystem manages high number of ranges its
performance become so poor that it freezes from time to time.
Solution:
Number of objects per slab should be increased taking into account maximal
slab size which can also be increased if needed.
Signed-off-by: Andrey Vesnovaty <andrey.vesnovaty@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#337
When comparing times gotten from ddi_get_lbolt, we have to take account of
wrap around of jiffies. Therefore, we cannot use 't1 < t2'. Instead we should
use 't1 - t2 < 0'.
This patch add ddi_time_after and friends to address this issue. They have
strict type restriction, clock_t for vanilla and int64_t for 64 version, to
prevent type conversion from screwing things.
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#335
This macro makes the compile to spit "mixed definition and code"
warning, I can't find a way to avoid it.
This patch lays some groundwork for the persistent l2arc feature.
See https://www.illumos.org/issues/3525.
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#303
There is plenty of compatibility code for a hw_hostid
that isn't used by anything. At the same time, there are apparently
issues with the current hostid logic. coredumb in #zfsonlinux on
freenode reported that Fedora 17 changes its hostid on every boot, which
required force importing his pool. A suggestion by wca was to adopt
FreeBSD's behavior, where it treats hostid as zero if /etc/hostid does
not exist
Adopting FreeBSD's behavior permits us to eliminate plenty of code,
including a userland helper that invokes the system's hostid as a
fallback.
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#224
The kernel's kthread_create() function is defined as "..." and there is
no va_list variant at the moment. The task name is pre-formatted into
a local buffer and passed to kthread_create() with fixed arguments.
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#347
The function was defined as a static inline with variable arguments
which causes gcc to generate errors on some distros.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes#346
Provide spl_kthread_create() as a wrapper to the kernel's kthread_create()
to provide pre-3.13 semantics. Re-try if the call is interrupted or if it
would have returned -ENOMEM. Otherwise return NULL.
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#339
Due to certain assumptions made in the the cred:groupmember test it
could result in false positives when run on specific distributions.
This was solely a bug in the test case and not in the groupmember()
function which the test case was validating.
To prevent future false positives the test case has been rewritten
to be both more rigerous and to make fewer assumptions about the
system.
Minor style cleanup was done to cr_groups_search() and groupmember()
functions.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
By setting __GFP_NORETRY the kernel memory reclaim logic was allowed to
abort early and dump a falled allocation stack to the console. Since
this was done in a tight loop to fill memory it could result in a large
number of stacks being dumped to the console. This in turn slowed down
the test sufficiently so it exceeded the time limit and failed.
To resolve this issue the __GFP_NORETRY flag is being removed. This is
how it should have been called originally to ensure we're simulating
the behavior of most callers which will use the GFP_KERNEL flag.
In addition, the reclaim granularity of 1000 objects was far to coarse
for this to be a realistic test. For kmem:slab_reclaim there might
only be a few thousand objects total in the cache. Therefore, the
SPLAT_KMEM_OBJ_RECLAIM constant for these tests was lowered. This
will cause the reclaim callback to run more frequently which makes
for a better test case.
The frequency of the cache reaping in kmem:slab_reap was increased
to accommodate the reduced number of objects released during the
reclaim.
These changes only impact the test cases and were done to remove
false positives caused by the test case itself.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Setting the 'dist_' prefix is the correct way to instruct Automake
to include these files in the distribution. The EXTRA_DIST variable
is reserved for files which are not covered by the automatic rules.
http://www.gnu.org/software/automake/manual/automake.html#Basics
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Add the minimum required ISA types to support the Sparc
architecture.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: marku89 <mar42@kola.li>
Closes#317
When this code was written it appears to have been assumed that
every taskq would have a large number of threads. In this case
it would make sense to attempt to evenly bind the threads over
all available CPUs. However, it failed to consider that creating
taskqs with a small number of threads will cause the CPUs with
lower ids become over-subscribed.
For this reason the kthread_bind() call is being removed and
we're leaving the kernel to schedule these threads as it sees fit.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#325
Related to issue #257 which added Linux 3.10 compatibility. For
ARM and Sparc architectures we must explicitly include the
<linux/vmalloc.h> header to ensure the vmalloc_info structure
is always defined when available.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #257Closes#291
Use the standard Linux MODULE_VERSION macro to expose the installed
spl and splat module versions. This will also automatically add a
checksum of the .c files and headers in "srcversion". See:
/sys/module/spl/version
/sys/module/spl/srcversion
/sys/module/splat/version
/sys/module/splat/srcversion
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closeszfsonlinux/zfs#1923
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This check was originally added for SLES10, a093c6a, to check for
a 'struct vfsmount *' argument which they added. However, since
SLES10 is based on a 2.6.16 kernel which is no longer supported
this functionality was dropped. The checks were refactored to
support Linux 3.13 without concern for historical versions.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#312
GCC 4.8.1 complained about an unused flags variable when building
against Linux 2.6.26.8:
/var/tmp/portage/sys-kernel/spl-9999/work/spl-9999/module/spl/../../module/spl/spl-condvar.c:
In function ‘__cv_init’:
/var/tmp/portage/sys-kernel/spl-9999/work/spl-9999/module/spl/../../module/spl/spl-condvar.c:39:6:
error: variable ‘flags’ set but not used
[-Werror=unused-but-set-variable]
int flags = KM_SLEEP;
^
cc1: all warnings being treated as errors
Additionally, the superfluous code uses a preempt_count variable that is
no longer available on Linux 3.13. Deleting the unnecessary code fixes a
Linux 3.13 compatibility issue.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#312
This is a first draft of a spl-module-parameters(5) man page. I have
just extracted the parameter name and its description with modinfo,
then checked the source what type it is and its default value.
This will need more work, preferably someone that actually know these
values and what to use them for. Similar to zfsonlinux/zfs#1856, but
for the spl.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closeszfsonlinux/zfs#1856
New versions of rpmbuild detect the invalid date which was added
incorrectly to the changelog. To silence this noise fix it.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#306
Make spl depend on the same version of spl-kmod, rather than on same or
better. When yum repository contains a number of versions the dependency
resolution breaks on trying to install non-latest version.
Signed-off-by: Cyril Plisko <cyril.plisko@mountall.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closeszfsonlinux/zfs#1677
torvalds/linux@24f7c6 introduced a new shrinker API while
torvalds/linux@a0b021 dropped support for the old shrinker API.
This patch adds support for the new shrinker API by wrapping
the old one with the new one.
This change also reorganizes the autotools checks on the shrinker
API such that the configure script will fail early if an unknown
API is encountered in the future.
Support for the set_shrinker() API which was used by Linux 2.6.22
and older has been dropped. As a general rule compatibility is
only maintained back to Linux 2.6.26.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/zfs#1732
Closes zfsonlinux/zfs#1822
Closes#293Closes#307
Needed for Illumos #3582. This interface is supposed to support
a variable-resolution timeout with nanosecond granularity. This
implementation rounds up to microsecond resolution, as nanosecond-
precision timing is rarely needed for real-world performance
tuning and may incur unnecessary busy-waiting. usleep_range() is
used if available, otherwise udelay() or msleep() are used
depending on the length of the delay interval.
Add flags from sys/callo.h as these are used to control the behavior of
cv_timedwait_hires(). Specifically,
CALLOUT_FLAG_ABSOLUTE
Normally, the expiration passed to the timeout API functions is
an expiration interval. If this flag is specified, then it is
interpreted as the expiration time itself.
CALLOUT_FLAG_ROUNDUP
Roundup the expiration time to the next resolution boundary. If this
flag is not specified, the expiration time is rounded down.
References:
https://www.illumos.org/issues/3582illumos/illumos-gate@0689f76
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#304
This branch updates the existing kstat infrastructure to be
more flexible. In particular, it extends the KSTAT_TYPE_RAW
type so it may be used to generate more dynamic kstats without
the need for additional custom types.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
These kstat interfaces are required to port
"Illumos #3537 want pool io kstats" to ZFS on Linux.
kstat_waitq_enter()
kstat_waitq_exit()
kstat_runq_enter()
kstat_runq_exit()
Additionally, zero out the ks_data buffer in __kstat_create() so
that the kstat_io_t counters are initialized to zero.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
While porting Illumos #3537 I found that ks_lock member of kstat_t
structure is different between Illumos and SPL. It is a pointer to
the kmutex_t in Illumos, but the mutex lock itself in SPL.
Apparently Illumos kstat API allows consumer to override the lock
if required. With SPL implementation it is not possible anymore.
Things were alright until the first attempt to actually override
the lock. Porting of Illumos #3537 introduced such code for the
first time.
In order to provide the Solaris/Illumos like functionality we:
1. convert ks_lock to "kmutex_t *ks_lock"
2. create a new field "kmutex_t ks_private_lock"
3. On kstat_create() ks_lock = &ks_private_lock
Thus if consumer doesn't care we still have our internal lock in use.
If, however, consumer does care she has a chance to set ks_lock to
anything else before calling kstat_install().
The rest of the code will use ks_lock regardless of its origin.
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #286
This reverts commit dba79fcbf2 in
favor of using the generic KSTAT_TYPE_RAW callbacks. The advantage
of this approach is that arbitrary types can be added without the
need to add them to the SPL.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #296
This change adds simple wrappers for accessing a thread's PID and
command character string.
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #296
The current implementation for displaying kstats of type KSTAT_TYPE_RAW
is rather crude. This patch attempts to enhance this handling by
allowing a kstat user to register formatting callbacks which can
optionally be used.
The callbacks allow the user to implement functions for interpreting
their data and transposing it into a character buffer. This buffer,
containing a string representation of the raw data, is then be displayed
through the current /proc textual interface.
Additionally the kstats are made writable because it's now possible
to provide a useful handler via the existing ks_update() interface.
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #296
It was observed that spl_kmem_cache_alloc() uses local_irq_save()
and saves the interrupt state in a local variable. This would
normally be fine except that spl_kmem_cache_alloc() calls
spl_cache_refill() which re-enables interrupts. It is then
possible that while interrupts are enabled the process is
rescheduled to a different cpu before being disable again.
This could result in us restoring the saved interrupt state
from one cpu to another.
What the consequences of this are aren't perfectly clear, but
this is clearly a bug and it has the potential to cause issues.
The code has been updated to just use local_irq_enable() and
local_irq_disable() to avoid this.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This is needed for the Illumos #4045 write throttle patch. It is used
in the arc eviction code to avoid blocking all arc activity by sitting on
arcs_mtx too long.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #286
