Update tuning so that it mentions maxusers, nmbclusters, and nsfbufs as

tunables in loader.conf rather than just kernel options.

MFC after: 3 days

1 files changed, 29 insertions, 18 deletions

diff --git a/share/man/man7/tuning.7 b/share/man/man7/tuning.7
index 821dd05..2b89105 100644
--- a/share/man/man7/tuning.7
+++ b/share/man/man7/tuning.7
@@ -369,28 +369,24 @@ rather then later, eating more swap and disk bandwidth.  In a small system
 this option will have a detrimental effect but in a large system that is
 already doing moderate paging this option allows the VM system to stage
 whole processes into and out of memory more easily.
-.Sh KERNEL CONFIG TUNING
-There are a number of kernel options that you may have to fiddle with in
-a large scale system.  In order to change these options you need to be
-able to compile a new kernel from source.  The
-.Xr config 8
-manual page and the handbook are good starting points for learning how to
-do this.  Generally the first thing you do when creating your own custom
-kernel is to strip out all the drivers and services you don't use.  Removing
-things like
-.Em INET6
-and drivers you don't have will reduce the size of your kernel, sometimes
-by a megabyte or more, leaving more memory available for applications.
+.Sh BOOT-TIME SYSCTL TUNING
+Some sysctls may not be tunable at runtime because the memory allocations
+they perform must occur early in the boot process.  To change these sysctls,
+you must set their value in
+.Xr loader.conf 5
+and reboot the system.
 .Pp
 The
-.Em maxusers
-kernel option defaults to an incredibly low value.  For most modern machines,
+.Em kern.maxusers
+sysctl defaults to an incredibly low value.  For most modern machines,
 you probably want to increase this value to 64, 128, or 256.  We do not
 recommend going above 256 unless you need a huge number of file descriptors.
 Network buffers are also affected but can be controlled with a separate
 kernel option.  Do not increase maxusers just to get more network mbufs.
+Systems older than FreeBSD 4.4 do not have this sysctl and require that
+the kernel config option maxusers be set instead.
 .Pp
-.Em NMBCLUSTERS
+.Em kern.ipc.nmbclusters
 may be adjusted to increase the number of network mbufs the system is
 willing to allocate.  Each cluster represents approximately 2K of memory,
 so a value of 1024 represents 2M of kernel memory reserved for network
@@ -399,19 +395,21 @@ If you have a web server which maxes out at 1000 simultaneous connections,
 and each connection eats a 16K receive and 16K send buffer, you need
 approximate 32MB worth of network buffers to deal with it.  A good rule of
 thumb is to multiply by 2, so 32MBx2 = 64MB/2K = 32768.  So for this case
-you would want to se NMBCLUSTERS to 32768.  We recommend values between
+you would want to set nmbclusters to 32768.  We recommend values between
 1024 and 4096 for machines with moderates amount of memory, and between 4096
 and 32768 for machines with greater amounts of memory.  Under no circumstances
 should you specify an arbitrarily high value for this parameter, it could
 lead to a boot-time crash.  The -m option to
 .Xr netstat 1
 may be used to observe network cluster use.
+Older versions of FreeBSD do not have this sysctl and require that the
+kernel config option NMBCLUSTERS be set instead.
 .Pp
 More and more programs are using the
 .Fn sendfile
 system call to transmit files over the network.  The
-.Em NSFBUFS
-kernel parameter controls the number of filesystem buffers
+.Em kern.ipc.nsfbufs
+sysctl controls the number of filesystem buffers
 .Fn sendfile
 is allowed to use to perform its work.  This parameter nominally scales
 with
@@ -419,6 +417,19 @@ with
 so you should not need to mess with this parameter except under extreme
 circumstances.
 .Pp
+.Sh KERNEL CONFIG TUNING
+There are a number of kernel options that you may have to fiddle with in
+a large scale system.  In order to change these options you need to be
+able to compile a new kernel from source.  The
+.Xr config 8
+manual page and the handbook are good starting points for learning how to
+do this.  Generally the first thing you do when creating your own custom
+kernel is to strip out all the drivers and services you don't use.  Removing
+things like
+.Em INET6
+and drivers you don't have will reduce the size of your kernel, sometimes
+by a megabyte or more, leaving more memory available for applications.
+.Pp
 .Em SCSI_DELAY
 and
 .Em IDE_DELAY