7a6b2b6429
On vnode backed md(4) devices over a certain, currently undetermined size relative to the buffer cache our "lemming-syncer" can provoke a buffer starvation which puts the md thread to sleep on wdrain. This generally tends to grind the entire system to a stop because the event that is supposed to wake up the thread will not happen until a fair bit of the piled up I/O requests in the system finish, and since a lot of those are on a md(4) vnode backed device which is currently waiting on wdrain until a fair amount of the piled up ... you get the picture. The cure is to issue all VOP_WRITES on the vnode backing the device with IO_SYNC. In addition to more closely emulating a real disk device with a non-lying write-cache, this makes the writes exempt from rate-limited (there to avoid starving the buffer cache) and consequently prevents the deadlock. Unfortunately performance takes a hit. Add "async" option to give people who know what they are doing the old behaviour.
225 lines
6.1 KiB
Groff
225 lines
6.1 KiB
Groff
.\" Copyright (c) 1993 University of Utah.
|
|
.\" Copyright (c) 1980, 1989, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\" Copyright (c) 2000
|
|
.\" Poul-Henning Kamp All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to Berkeley by
|
|
.\" the Systems Programming Group of the University of Utah Computer
|
|
.\" Science Department.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)vnconfig.8 8.1 (Berkeley) 6/5/93
|
|
.\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd December 31, 2000
|
|
.Dt MDCONFIG 8
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mdconfig
|
|
.Nd configure and enable memory disks
|
|
.Sh SYNOPSIS
|
|
.Nm
|
|
.Fl a
|
|
.Fl t Ar type
|
|
.Op Fl n
|
|
.Oo
|
|
.Fl o
|
|
.Oo Cm no Oc Ns Ar option
|
|
.Oc
|
|
.Op Fl s Ar size
|
|
.Op Fl f Ar file
|
|
.Op Fl S Ar sectorsize
|
|
.Op Fl u Ar unit
|
|
.Op Fl x Ar sectors/track
|
|
.Op Fl y Ar heads/cyl
|
|
.Nm
|
|
.Fl d
|
|
.Fl u Ar unit
|
|
.Nm
|
|
.Fl l
|
|
.Op Fl n
|
|
.Op Fl u Ar unit
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
utility configures and enables
|
|
.Xr md 4
|
|
devices.
|
|
.Pp
|
|
Options indicate an action to be performed:
|
|
.Bl -tag -width indent
|
|
.It Fl a
|
|
Attach a memory disk.
|
|
This will configure and attach a memory disk with the
|
|
parameters specified and attach it to the system.
|
|
.It Fl d
|
|
Detach a memory disk from the system and release all resources.
|
|
.It Fl t Ar type
|
|
Select the type of the memory disk.
|
|
.Bl -tag -width "preload"
|
|
.It Cm malloc
|
|
Storage for this type of memory disk is allocated with
|
|
.Xr malloc 9 .
|
|
This limits the size to the malloc bucket limit in the kernel.
|
|
If the
|
|
.Fl o Cm reserve
|
|
option is not set, creating and filling a large
|
|
malloc-backed memory disk is a very easy way to
|
|
panic a system.
|
|
.It Cm vnode
|
|
A file specified with
|
|
.Fl f Ar file
|
|
becomes the backingstore for this memory disk.
|
|
.It Cm swap
|
|
swapspace is used to back this memory disk.
|
|
.El
|
|
.It Fl f Ar file
|
|
Filename to use for the vnode type memory disk.
|
|
.It Fl l
|
|
List information about configured
|
|
.Xr md 4
|
|
devices. If the
|
|
.Fl u
|
|
option is used in conjuction with this, the output is limited to
|
|
information on the specified device.
|
|
.It Fl n
|
|
When printing md device names, print only the unit number without the
|
|
md prefix.
|
|
.It Fl s Ar size
|
|
Size of the memory disk.
|
|
.Ar Size
|
|
is the number of 512 byte sectors unless suffixed with a
|
|
.Cm k , m ,
|
|
or
|
|
.Cm g
|
|
which
|
|
denotes kilobyte, megabyte and gigabyte respectively.
|
|
.It Fl S Ar sectorsize
|
|
Sectorsize to use for malloc backed device.
|
|
.It Fl x Ar sectors/track
|
|
See description of
|
|
.Fl y
|
|
below.
|
|
.It Fl y Ar heads/cylinder
|
|
For malloc or vnode backed devices, the
|
|
.Fl x
|
|
and
|
|
.Fl y
|
|
options can be used to specify a synthetic geometry.
|
|
This is useful for constructing bootable images for later download to
|
|
other devices.
|
|
.It Fl o Oo Cm no Oc Ns Ar option
|
|
Set or reset options.
|
|
.Bl -tag -width indent
|
|
.It Oo Cm no Oc Ns Cm async
|
|
For vnode backed devices: avoid IO_SYNC for increased performance but
|
|
at the risk of deadlocking the entire kernel.
|
|
.It Oo Cm no Oc Ns Cm reserve
|
|
Allocate and reserve all needed storage from the start, rather than as needed.
|
|
.It Oo Cm no Oc Ns Cm cluster
|
|
Enable clustering on this disk.
|
|
.It Oo Cm no Oc Ns Cm compress
|
|
Enable/Disable compression features to reduce memory usage.
|
|
.It Oo Cm no Oc Ns Cm force
|
|
Disable/Enable extra sanity checks to prevent the user from doing something
|
|
that might adversely affect the system.
|
|
.It Oo Cm no Oc Ns Cm readonly
|
|
Enable/Disable readonly mode.
|
|
.El
|
|
.It Fl u Ar unit
|
|
Request a specific unit number for the
|
|
.Xr md 4
|
|
device instead of automatic allocation.
|
|
.El
|
|
.Sh EXAMPLES
|
|
To create a 4 megabyte
|
|
.Xr malloc 9
|
|
backed memory disk.
|
|
The name of the allocated unit will be output on stdout like
|
|
.Dq Li md3 :
|
|
.Pp
|
|
.Dl mdconfig -a -t malloc -s 4m
|
|
.Pp
|
|
To create a disk named
|
|
.Pa /dev/md4
|
|
with
|
|
.Pa /tmp/boot.flp
|
|
as backing:
|
|
.Pp
|
|
.Dl mdconfig -a -t vnode -f /tmp/boot.flp -u 4
|
|
.Pp
|
|
To detach and free all resources used by
|
|
.Pa /dev/md4 :
|
|
.Pp
|
|
.Dl mdconfig -d -u 4
|
|
.Pp
|
|
To create and mount a 128MByte swap backed file system on
|
|
.Pa /tmp :
|
|
.Bd -literal -offset indent
|
|
mdconfig -a -t swap -s 128M -u 10
|
|
newfs -U /dev/md10
|
|
mount /dev/md10 /tmp
|
|
chmod 1777 /tmp
|
|
.Ed
|
|
.Pp
|
|
To create a 5MB file-backed disk:
|
|
.Bd -literal -offset indent
|
|
dd if=/dev/zero of=somebackingfile bs=1k count=5k
|
|
mdconfig -a -t vnode -f somebackingfile -u 0
|
|
bsdlabel -w md0 auto
|
|
newfs md0c
|
|
mount /dev/md0c /mnt
|
|
.Ed
|
|
.Sh SEE ALSO
|
|
.Xr md 4 ,
|
|
.Xr bsdlabel 8 ,
|
|
.Xr fdisk 8 ,
|
|
.Xr mdmfs 8 ,
|
|
.Xr malloc 9
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
utility first appeared in
|
|
.Fx 5.0
|
|
as a cleaner replacement for the
|
|
.Xr vn 4
|
|
and
|
|
.Xr vnconfig 8
|
|
combo.
|
|
.Sh AUTHORS
|
|
The
|
|
.Nm
|
|
utility was written by
|
|
.An Poul-Henning Kamp
|
|
.Aq phk@FreeBSD.org .
|