kernel memory allocator
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share/man/man9/malloc.9
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share/man/man9/malloc.9
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.\" $NetBSD: malloc.9,v 1.1 1996/06/16 23:20:53 pk Exp $
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.\"
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd Jun 16, 1996
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.Dt MALLOC 9
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.Os NetBSD
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.Sh NAME
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.Nm malloc
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.Nd kernel memory allocator
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.Sh SYNOPSIS
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.Ft void *
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.Fn malloc "unsigned long size" "int type" "int flags"
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.Fn MALLOC "space" "cast" "unsigned long size" "int type" "int flags"
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.Ft void
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.Fn free "void *addr" "int type"
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.Fn FREE "void *addr" "int type"
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.Sh DESCRIPTION
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The
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.Fn malloc
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function allocates uninitialized memory in kernel address space for an
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object whose size is specified by
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.Fa size .
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.Fn free
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releases memory at address
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.Fa addr
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that was previously allocated by
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.Fn malloc
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for re-use.
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The
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.Fn MALLOC
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macro variant is functionally equivalent to
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.Bd -literal -offset indent
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(space) = (cast)malloc((u_long)(size), type, flags)
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.Ed
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.Pp
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and the
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.Fn FREE
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macro variant is equivalent to
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.Bd -literal -offset indent
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free((caddr_t)(addr), type)
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.Ed
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.Pp
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Unlike its standard C library counterpart
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.Pq Xr malloc 3 ,
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the kernel version takes two more arguments. The
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.Fa flags
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argument further qualifies
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.Fn malloc No Ns 's
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operational charateristics as follows:
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.Bl -tag -offset indent
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.It Dv M_NOWAIT
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Causes
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.Fn malloc to return
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.Dv NULL
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if the request cannot be immediately fulfilled due to resource shortage.
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Otherwise,
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.Fn malloc
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may call sleep to wait for resources to be released by other processes.
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If this flag is not set,
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.Fn malloc
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will never return
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.Dv NULL .
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Note that
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.Dv M_WAITOK
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is conveniently defined to be 0, and hence maybe or'ed into the
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.Fa flags
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argument to indicate that it's Ok to wait for resources.
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.El
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.Pp
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Currently, only one flag is defined.
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.Pp
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The
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.Fa type
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argument broadly identifies the the kernel subsystem for which the allocated
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memory was needed, and is commonly used to maintain statistics about
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kernel memory usage. The following types are currently defined:
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.Pp
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.Bl -tag -offset indent -width XXXXXXXXXXXXXX -compact
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.It Dv M_FREE
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Should be on free list.
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.It Dv M_MBUF
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Mbuf memory.
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.It Dv M_DEVBUF
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Device driver memory.
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.It Dv M_SOCKET
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Socket structure.
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.It Dv M_PCB
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Protocol control block.
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.It Dv M_RTABLE
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Routing tables.
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.It Dv M_HTABLE
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IMP host tables.
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.It Dv M_FTABLE
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Fragment reassembly header.
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.It Dv M_ZOMBIE
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Zombie proc status
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.It Dv M_IFADDR
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Interface address.
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.It Dv M_SOOPTS
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Socket options.
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.It Dv M_SONAME
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Socket name.
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.It Dv M_NAMEI
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Namei path name buffer.
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.It Dv M_GPROF
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Kernel profiling buffer.
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.It Dv M_IOCTLOPS
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Ioctl data buffer.
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.It Dv M_MAPMEM
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Mapped memory descriptors.
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.It Dv M_CRED
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Credentials.
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.It Dv M_PGRP
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Process group header.
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.It Dv M_SESSION
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Session header.
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.It Dv M_IOV
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Large iov's.
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.It Dv M_MOUNT
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Vfs mount struct.
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.It Dv M_FHANDLE
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Network file handle.
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.It Dv M_NFSREQ
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NFS request header.
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.It Dv M_NFSMNT
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NFS mount structure.
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.It Dv M_NFSNODE
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NFS vnode private part.
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.It Dv M_VNODE
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Dynamically allocated vnodes.
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.It Dv M_CACHE
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Dynamically allocated cache entries.
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.It Dv M_DQUOT
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UFS quota entries.
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.It Dv M_UFSMNT
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UFS mount structure.
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.It Dv M_SHM
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SVID compatible shared memory segments.
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.It Dv M_VMMAP
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VM map structures.
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.It Dv M_VMMAPENT
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VM map entry structures.
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.It Dv M_VMOBJ
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VM object structure.
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.It Dv M_VMOBJHASH
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VM object hash structure.
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.It Dv M_VMPMAP
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VM pmap.
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.It Dv M_VMPVENT
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VM phys-virt mapping entry.
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.It Dv M_VMPAGER
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XXX: VM pager struct.
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.It Dv M_VMPGDATA
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XXX: VM pager private data.
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.It Dv M_FILE
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Open file structure.
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.It Dv M_FILEDESC
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Open file descriptor table.
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.It Dv M_LOCKF
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Byte-range locking structures.
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.It Dv M_PROC
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Proc structures.
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.It Dv M_SUBPROC
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Proc sub-structures.
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.It Dv M_SEGMENT
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Segment for LFS.
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.It Dv M_LFSNODE
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LFS vnode private part.
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.It Dv M_FFSNODE
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FFS vnode private part.
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.It Dv M_MFSNODE
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MFS vnode private part.
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.It Dv M_NQLEASE
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Nqnfs lease.
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.It Dv M_NQMHOST
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Nqnfs host address table.
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.It Dv M_NETADDR
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Export host address structure.
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.It Dv M_NFSSVC
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Nfs server structure.
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.It Dv M_NFSUID
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Nfs uid mapping structure.
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.It Dv M_NFSD
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Nfs server daemon structure.
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.It Dv M_IPMOPTS
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Internet multicast options.
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.It Dv M_IPMADDR
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Internet multicast address.
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.It Dv M_IFMADDR
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Link-level multicast address.
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.It Dv M_MRTABLE
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Multicast routing tables.
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.It Dv M_ISOFSMNT
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ISOFS mount structure.
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.It Dv M_ISOFSNODE
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ISOFS vnode private part.
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.It Dv M_MSDOSFSMNT
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MSDOS FS mount structure.
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.It Dv M_MSDOSFSFAT
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MSDOS FS fat table.
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.It Dv M_MSDOSFSNODE
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MSDOS FS vnode private part.
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.It Dv M_TTYS
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Allocated tty structures.
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.It Dv M_EXEC
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Argument lists & other mem used by exec.
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.It Dv M_MISCFSMNT
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Miscfs mount structures.
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.It Dv M_MISCFSNODE
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Miscfs vnode private part.
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.It Dv M_ADOSFSMNT
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Adosfs mount structures.
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.It Dv M_ADOSFSNODE
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ADosfs vnode private part.
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.It Dv M_ANODE
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Adosfs anode structures and tables.
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.It Dv M_IPQ
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IP packet queue entry.
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.It Dv M_AFS
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Andrew File System.
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.It Dv M_ADOSFSBITMAP
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Adosfs bitmap.
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.It Dv M_TEMP
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Misc temporary data buffers.
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.El
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.Pp
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Statistics based on the
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.Fa type
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argument is maintained only if the kernel option
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.Dv KMEMSTATS
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is used when compiling the kernel
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.Po the default in current
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.Nx
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kernels
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.Pc
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and can be examined by using
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.Sq vmstat -m .
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.Sh RETURN VALUES
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.Fn malloc
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returns a kernel virtual address that is suitably aligned for storage of
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any type of object.
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.Sh SEE ALSO
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.Xr vmstat 8
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.Sh DIAGNOSTICS
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A kernel compiled with the
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.Dv DIAGNOSTIC
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configuration option attempts to detect detect memory corruption caused by
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such things as writing outside the allocated area and imbalanced calls to the
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.Fn malloc
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and
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.Fn free
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functions. Failing consistency checks will cause a panic or a system console
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message:
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.Bl -bullet -offset indent -compact
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.Pp
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.It
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panic:
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.Dq malloc - bogus type
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.It
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panic:
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.Dq malloc: out of space in kmem_map
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.It
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panic:
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.Dq malloc: allocation too large
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.It
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panic:
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.Dq malloc: wrong bucket
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.It
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panic:
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.Dq malloc: lost data
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.It
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panic:
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.Dq free: unaligned addr
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.It
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panic:
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.Dq free: duplicated free
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.It
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panic:
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.Dq free: multiple frees
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.It
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panic:
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.Dq init: minbucket too small/struct freelist too big
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.It
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.Dq multiply freed item Aq addr
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.It
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.Dq Data modified on freelist: Aq data object description
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.El
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