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Modernise/fix/rewrite unlinted manpages

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zpool-destroy.8: flatten, fix description
zfs-wait.8: flatten, fix description, use list for events
zpool-reguid.8: flatten, fix description
zpool-history.8: flatten, fix description
zpool-export.8: flatten, fix description, remove -f "unmount" reference
  AFAICT no such command exists even in Illumos (as of today, anyway),
  and we definitely don't call it
zpool-labelclear.8: flatten, fix description
zpool-features.5: modernise
spl-module-parameters.5: modernise
zfs-mount-generator.8: rewrite
zfs-module-parameters.5: modernise

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12169
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2021-06-07 21:41:54 +02:00
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man/man5/spl-module-parameters.5
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'\" te
.\"
.\" The contents of this file are subject to the terms of the Common Development
.\" and Distribution License (the "License"). You may not use this file except
.\" in compliance with the License. You can obtain a copy of the license at
.\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.
.\"
.\" See the License for the specific language governing permissions and
.\" limitations under the License. When distributing Covered Code, include this
.\" CDDL HEADER in each file and include the License file at
.\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this
.\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
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.\" Copyright 2013 Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
.\"
.TH SPL-MODULE-PARAMETERS 5 "Aug 24, 2020" OpenZFS
.SH NAME
spl\-module\-parameters \- SPL module parameters
.SH DESCRIPTION
.sp
.LP
Description of the different parameters to the SPL module.
.SS "Module parameters"
.sp
.LP
.sp
.ne 2
.na
\fBspl_kmem_cache_kmem_threads\fR (uint)
.ad
.RS 12n
The number of threads created for the spl_kmem_cache task queue. This task
queue is responsible for allocating new slabs for use by the kmem caches.
.Dd August 24, 2020
.Dt SPL-MODULE-PARAMETERS 5
.Os
.
.Sh NAME
.Nm spl-module-parameters
.Nd parameters of the SPL kernel module
.
.Sh DESCRIPTION
.Bl -tag -width Ds
.It Sy spl_kmem_cache_kmem_threads Ns = Ns Sy 4 Pq uint
The number of threads created for the spl_kmem_cache task queue.
This task queue is responsible for allocating new slabs
for use by the kmem caches.
For the majority of systems and workloads only a small number of threads are
required.
.sp
Default value: \fB4\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_cache_reclaim\fR (uint)
.ad
.RS 12n
.
.It Sy spl_kmem_cache_reclaim Ns = Ns Sy 0 Pq uint
When this is set it prevents Linux from being able to rapidly reclaim all the
memory held by the kmem caches. This may be useful in circumstances where
it's preferable that Linux reclaim memory from some other subsystem first.
memory held by the kmem caches.
This may be useful in circumstances where it's preferable that Linux
reclaim memory from some other subsystem first.
Setting this will increase the likelihood out of memory events on a memory
constrained system.
.sp
Default value: \fB0\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_cache_obj_per_slab\fR (uint)
.ad
.RS 12n
The preferred number of objects per slab in the cache. In general, a larger
value will increase the caches memory footprint while decreasing the time
required to perform an allocation. Conversely, a smaller value will minimize
the footprint and improve cache reclaim time but individual allocations may
take longer.
.sp
Default value: \fB8\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_cache_max_size\fR (uint)
.ad
.RS 12n
The maximum size of a kmem cache slab in MiB. This effectively limits
the maximum cache object size to \fBspl_kmem_cache_max_size\fR /
\fBspl_kmem_cache_obj_per_slab\fR. Caches may not be created with
.
.It Sy spl_kmem_cache_obj_per_slab Ns = Ns Sy 8 Pq uint
The preferred number of objects per slab in the cache.
In general, a larger value will increase the caches memory footprint
while decreasing the time required to perform an allocation.
Conversely, a smaller value will minimize the footprint
and improve cache reclaim time but individual allocations may take longer.
.
.It Sy spl_kmem_cache_max_size Ns = Ns Sy 32 Po 64-bit Pc or Sy 4 Po 32-bit Pc Pq uint
The maximum size of a kmem cache slab in MiB.
This effectively limits the maximum cache object size to
.Sy spl_kmem_cache_max_size Ns / Ns Sy spl_kmem_cache_obj_per_slab .
.Pp
Caches may not be created with
object sized larger than this limit.
.sp
Default value: \fB32 (64-bit) or 4 (32-bit)\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_cache_slab_limit\fR (uint)
.ad
.RS 12n
.
.It Sy spl_kmem_cache_slab_limit Ns = Ns Sy 16384 Pq uint
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. This
value is used to determine the cutoff between a small and large object.
.sp
Objects of \fBspl_kmem_cache_slab_limit\fR or smaller will be allocated
using the Linux slab allocator, large objects use the SPL allocator. A
cutoff of 16K was determined to be optimal for architectures using 4K pages.
.sp
Default value: \fB16,384\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_alloc_warn\fR (uint)
.ad
.RS 12n
As a general rule kmem_alloc() allocations should be small, preferably
just a few pages since they must by physically contiguous. Therefore, a
rate limited warning will be printed to the console for any kmem_alloc()
efficient use of the memory.
However, large objects are not supported by
the Linux slab and therefore the SPL implementation is preferred.
This value is used to determine the cutoff between a small and large object.
.Pp
Objects of size
.Sy spl_kmem_cache_slab_limit
or smaller will be allocated using the Linux slab allocator,
large objects use the SPL allocator.
A cutoff of 16K was determined to be optimal for architectures using 4K pages.
.
.It Sy spl_kmem_alloc_warn Ns = Ns Sy 32768 Pq uint
As a general rule
.Fn kmem_alloc
allocations should be small,
preferably just a few pages, since they must by physically contiguous.
Therefore, a rate limited warning will be printed to the console for any
.Fn kmem_alloc
which exceeds a reasonable threshold.
.sp
.Pp
The default warning threshold is set to eight pages but capped at 32K to
accommodate systems using large pages. This value was selected to be small
enough to ensure the largest allocations are quickly noticed and fixed.
accommodate systems using large pages.
This value was selected to be small enough to ensure
the largest allocations are quickly noticed and fixed.
But large enough to avoid logging any warnings when a allocation size is
larger than optimal but not a serious concern. Since this value is tunable,
developers are encouraged to set it lower when testing so any new largish
allocations are quickly caught. These warnings may be disabled by setting
the threshold to zero.
.sp
Default value: \fB32,768\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_alloc_max\fR (uint)
.ad
.RS 12n
Large kmem_alloc() allocations will fail if they exceed KMALLOC_MAX_SIZE.
larger than optimal but not a serious concern.
Since this value is tunable, developers are encouraged to set it lower
when testing so any new largish allocations are quickly caught.
These warnings may be disabled by setting the threshold to zero.
.
.It Sy spl_kmem_alloc_max Ns = Ns Sy KMALLOC_MAX_SIZE Ns / Ns Sy 4 Pq uint
Large
.Fn kmem_alloc
allocations will fail if they exceed
.Sy KMALLOC_MAX_SIZE .
Allocations which are marginally smaller than this limit may succeed but
should still be avoided due to the expense of locating a contiguous range
of free pages. Therefore, a maximum kmem size with reasonable safely
margin of 4x is set. Kmem_alloc() allocations larger than this maximum
will quickly fail. Vmem_alloc() allocations less than or equal to this
value will use kmalloc(), but shift to vmalloc() when exceeding this value.
.sp
Default value: \fBKMALLOC_MAX_SIZE/4\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_cache_magazine_size\fR (uint)
.ad
.RS 12n
of free pages.
Therefore, a maximum kmem size with reasonable safely margin of 4x is set.
.Fn kmem_alloc
allocations larger than this maximum will quickly fail.
.Fn vmem_alloc
allocations less than or equal to this value will use
.Fn kmalloc ,
but shift to
.Fn vmalloc
when exceeding this value.
.
.It Sy spl_kmem_cache_magazine_size Ns = Ns Sy 0 Pq uint
Cache magazines are an optimization designed to minimize the cost of
allocating memory. They do this by keeping a per-cpu cache of recently
freed objects, which can then be reallocated without taking a lock. This
can improve performance on highly contended caches. However, because
objects in magazines will prevent otherwise empty slabs from being
immediately released this may not be ideal for low memory machines.
.sp
For this reason \fBspl_kmem_cache_magazine_size\fR can be used to set a
maximum magazine size. When this value is set to 0 the magazine size will
be automatically determined based on the object size. Otherwise magazines
will be limited to 2-256 objects per magazine (i.e per cpu). Magazines
may never be entirely disabled in this implementation.
.sp
Default value: \fB0\fR
.RE
.sp
.ne 2
.na
\fBspl_hostid\fR (ulong)
.ad
.RS 12n
allocating memory.
They do this by keeping a per-cpu cache of recently
freed objects, which can then be reallocated without taking a lock.
This can improve performance on highly contended caches.
However, because objects in magazines will prevent otherwise empty slabs
from being immediately released this may not be ideal for low memory machines.
.Pp
For this reason,
.Sy spl_kmem_cache_magazine_size
can be used to set a maximum magazine size.
When this value is set to 0 the magazine size will
be automatically determined based on the object size.
Otherwise magazines will be limited to 2-256 objects per magazine (i.e per cpu).
Magazines may never be entirely disabled in this implementation.
.
.It Sy spl_hostid Ns = Ns Sy 0 Pq ulong
The system hostid, when set this can be used to uniquely identify a system.
By default this value is set to zero which indicates the hostid is disabled.
It can be explicitly enabled by placing a unique non-zero value in
\fB/etc/hostid/\fR.
.sp
Default value: \fB0\fR
.RE
.sp
.ne 2
.na
\fBspl_hostid_path\fR (charp)
.ad
.RS 12n
The expected path to locate the system hostid when specified. This value
may be overridden for non-standard configurations.
.sp
Default value: \fB/etc/hostid\fR
.RE
.sp
.ne 2
.na
\fBspl_panic_halt\fR (uint)
.ad
.RS 12n
Cause a kernel panic on assertion failures. When not enabled, the thread is
halted to facilitate further debugging.
.sp
.Pa /etc/hostid .
.
.It Sy spl_hostid_path Ns = Ns Pa /etc/hostid Pq charp
The expected path to locate the system hostid when specified.
This value may be overridden for non-standard configurations.
.
.It Sy spl_panic_halt Ns = Ns Sy 0 Pq uint
Cause a kernel panic on assertion failures.
When not enabled, the thread is halted to facilitate further debugging.
.Pp
Set to a non-zero value to enable.
.sp
Default value: \fB0\fR
.RE
.sp
.ne 2
.na
\fBspl_taskq_kick\fR (uint)
.ad
.RS 12n
Kick stuck taskq to spawn threads. When writing a non-zero value to it, it will
scan all the taskqs. If any of them have a pending task more than 5 seconds old,
it will kick it to spawn more threads. This can be used if you find a rare
.
.It Sy spl_taskq_kick Ns = Ns Sy 0 Pq uint
Kick stuck taskq to spawn threads.
When writing a non-zero value to it, it will scan all the taskqs.
If any of them have a pending task more than 5 seconds old,
it will kick it to spawn more threads.
This can be used if you find a rare
deadlock occurs because one or more taskqs didn't spawn a thread when it should.
.sp
Default value: \fB0\fR
.RE
.sp
.ne 2
.na
\fBspl_taskq_thread_bind\fR (int)
.ad
.RS 12n
Bind taskq threads to specific CPUs. When enabled all taskq threads will
be distributed evenly over the available CPUs. By default, this behavior
is disabled to allow the Linux scheduler the maximum flexibility to determine
where a thread should run.
.sp
Default value: \fB0\fR
.RE
.sp
.ne 2
.na
\fBspl_taskq_thread_dynamic\fR (int)
.ad
.RS 12n
Allow dynamic taskqs. When enabled taskqs which set the TASKQ_DYNAMIC flag
will by default create only a single thread. New threads will be created on
demand up to a maximum allowed number to facilitate the completion of
outstanding tasks. Threads which are no longer needed will be promptly
destroyed. By default this behavior is enabled but it can be disabled to
.
.It Sy spl_taskq_thread_bind Ns = Ns Sy 0 Pq int
Bind taskq threads to specific CPUs.
When enabled all taskq threads will be distributed evenly
across the available CPUs.
By default, this behavior is disabled to allow the Linux scheduler
the maximum flexibility to determine where a thread should run.
.
.It Sy spl_taskq_thread_dynamic Ns = Ns Sy 1 Pq int
Allow dynamic taskqs.
When enabled taskqs which set the
.Sy TASKQ_DYNAMIC
flag will by default create only a single thread.
New threads will be created on demand up to a maximum allowed number
to facilitate the completion of outstanding tasks.
Threads which are no longer needed will be promptly destroyed.
By default this behavior is enabled but it can be disabled to
aid performance analysis or troubleshooting.
.sp
Default value: \fB1\fR
.RE
.sp
.ne 2
.na
\fBspl_taskq_thread_priority\fR (int)
.ad
.RS 12n
.
.It Sy spl_taskq_thread_priority Ns = Ns Sy 1 Pq int
Allow newly created taskq threads to set a non-default scheduler priority.
When enabled the priority specified when a taskq is created will be applied
to all threads created by that taskq. When disabled all threads will use
the default Linux kernel thread priority. By default, this behavior is
enabled.
.sp
Default value: \fB1\fR
.RE
.sp
.ne 2
.na
\fBspl_taskq_thread_sequential\fR (int)
.ad
.RS 12n
When enabled, the priority specified when a taskq is created will be applied
to all threads created by that taskq.
When disabled all threads will use the default Linux kernel thread priority.
By default, this behavior is enabled.
.
.It Sy spl_taskq_thread_sequential Ns = Ns Sy 4 Pq int
The number of items a taskq worker thread must handle without interruption
before requesting a new worker thread be spawned. This is used to control
before requesting a new worker thread be spawned.
This is used to control
how quickly taskqs ramp up the number of threads processing the queue.
Because Linux thread creation and destruction are relatively inexpensive a
small default value has been selected. This means that normally threads will
be created aggressively which is desirable. Increasing this value will
small default value has been selected.
This means that normally threads will be created aggressively which is desirable.
Increasing this value will
result in a slower thread creation rate which may be preferable for some
configurations.
.sp
Default value: \fB4\fR
.RE
.sp
.ne 2
.na
\fBspl_max_show_tasks\fR (uint)
.ad
.RS 12n
.
.It Sy spl_max_show_tasks Ns = Ns Sy 512 Pq uint
The maximum number of tasks per pending list in each taskq shown in
/proc/spl/{taskq,taskq-all}. Write 0 to turn off the limit. The proc file will
walk the lists with lock held, reading it could cause a lock up if the list
grow too large without limiting the output. "(truncated)" will be shown if the
list is larger than the limit.
.sp
Default value: \fB512\fR
.RE
.Pa /proc/spl/taskq{,-all} .
Write
.Sy 0
to turn off the limit.
The proc file will walk the lists with lock held,
reading it could cause a lock-up if the list grow too large
without limiting the output.
"(truncated)" will be shown if the list is larger than the limit.
.
.El
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