351 lines
10 KiB
Groff
351 lines
10 KiB
Groff
.\"
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.\" Copyright (c) 2003 Bruce M Simpson <bms@spc.org>
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.\" All rights reserved.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 9, 2011
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.Dt VM_MAP 9
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.Os
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.Sh NAME
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.Nm vm_map
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.Nd virtual address space portion of virtual memory subsystem
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.Sh SYNOPSIS
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.In sys/param.h
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.In vm/vm.h
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.In vm/vm_map.h
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.Sh DESCRIPTION
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The
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.Nm
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subsystem is used to manage virtual address spaces.
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This section describes the main data structures used within the code.
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.Pp
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The
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.Vt "struct vm_map"
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is a generic representation of an address space.
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This address space may belong to a user process or the kernel.
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The kernel actually uses several maps, which are maintained as
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subordinate maps, created using the
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.Xr vm_map_submap 9
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function.
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.Bd -literal -offset indent
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struct vm_map {
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struct vm_map_entry header;
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struct sx lock;
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struct mtx system_mtx;
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int nentries;
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vm_size_t size;
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u_int timestamp;
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u_char needs_wakeup;
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u_char system_map;
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vm_flags_t flags;
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vm_map_entry_t root;
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pmap_t pmap;
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#define min_offset header.start
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#define max_offset header.end
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};
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.Ed
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.Pp
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The fields of
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.Vt struct vm_map
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are as follows:
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.Bl -tag -width ".Va needs_wakeup"
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.It Va header
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Head node of a circular, doubly linked list of
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.Vt struct vm_map_entry
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objects.
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Each object defines a particular region within this map's address space.
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.It Va lock
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Used to serialize access to the structure.
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.It Va system_mtx
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A mutex which is used if the map is a system map.
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.It Va nentries
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A count of the members in use within the circular map entry list.
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.It Va size
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Specifies the size of the virtual address space.
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.It Va timestamp
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Used to determine if the map has changed since its last access.
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.It Va needs_wakeup
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Indicates if a thread is waiting for an allocation within the map.
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Used only by system maps.
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.It Va system_map
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Set to TRUE to indicate that map is a system map; otherwise, it belongs
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to a user process.
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.It Va flags
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Map flags, described below.
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.It Va root
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Root node of a binary search tree used for fast lookup of map entries.
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.It Va pmap
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Pointer to the underlying physical map with which this virtual map
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is associated.
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.It Va min_offset
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The minimum
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.Vt vm_offset_t
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in this map.
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Programs should never use
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.Va header.start
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or
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.Va header.end
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directly, use
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.Va min_offset
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and
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.Va max_offset
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instead.
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.It Va max_offset
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The maximum
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.Vt vm_offset_t
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in this map.
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.El
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.Pp
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There is one possible map flag:
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.Bl -tag -width ".Dv MAP_PREFAULT_MADVISE"
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.It Dv MAP_WIREFUTURE
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Wire all future pages in this map.
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.El
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.Pp
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The following flags can be passed to
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.Xr vm_map_find 9
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and
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.Xr vm_map_insert 9
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to specify the copy-on-write properties of regions within the map:
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.Bl -tag -width ".Dv MAP_PREFAULT_MADVISE"
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.It Dv MAP_COPY_ON_WRITE
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The mapping is copy-on-write.
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.It Dv MAP_NOFAULT
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The mapping should not generate page faults.
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.It Dv MAP_PREFAULT
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The mapping should be prefaulted into physical memory.
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.It Dv MAP_PREFAULT_PARTIAL
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The mapping should be partially prefaulted into physical memory.
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.It Dv MAP_DISABLE_SYNCER
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Do not periodically flush dirty pages; only flush them when absolutely
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necessary.
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.It Dv MAP_DISABLE_COREDUMP
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Do not include the mapping in a core dump.
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.It Dv MAP_PREFAULT_MADVISE
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Specify that the request is from a user process calling
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.Xr madvise 2 .
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.It Dv MAP_ACC_CHARGED
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Region is already charged to the requestor by some means.
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.It Dv MAP_ACC_NO_CHARGE
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Do not charge for allocated region.
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.El
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.Pp
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The
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.Vt struct vm_map_entry
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is a generic representation of a region.
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The region managed by each entry is associated with a
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.Vt union vm_map_object ,
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described below.
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.Bd -literal -offset indent
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struct vm_map_entry {
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struct vm_map_entry *prev;
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struct vm_map_entry *next;
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struct vm_map_entry *left;
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struct vm_map_entry *right;
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vm_offset_t start;
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vm_offset_t end;
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vm_offset_t avail_ssize;
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vm_size_t adj_free;
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vm_size_t max_free;
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union vm_map_object object;
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vm_ooffset_t offset;
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vm_eflags_t eflags;
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/* Only in task maps: */
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vm_prot_t protection;
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vm_prot_t max_protection;
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vm_inherit_t inheritance;
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int wired_count;
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vm_pindex_t lastr;
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};
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.Ed
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.Pp
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The fields of
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.Vt struct vm_map_entry
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are as follows:
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.Bl -tag -width ".Va avail_ssize"
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.It Va prev
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Pointer to the previous node in a doubly-linked, circular list.
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.It Va next
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Pointer to the next node in a doubly-linked, circular list.
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.It Va left
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Pointer to the left node in a binary search tree.
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.It Va right
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Pointer to the right node in a binary search tree.
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.It Va start
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Lower address bound of this entry's region.
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.It Va end
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Upper address bound of this entry's region.
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.It Va avail_ssize
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If the entry is for a process stack, specifies how much the entry can grow.
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.It Va adj_free
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The amount of free, unmapped address space adjacent to and immediately
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following this map entry.
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.It Va max_free
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The maximum amount of contiguous free space in this map entry's subtree.
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.It Va object
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Pointer to the
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.Vt struct vm_map_object
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with which this entry is associated.
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.It Va offset
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Offset within the
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.Va object
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which is mapped from
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.Va start
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onwards.
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.It Va eflags
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Flags applied to this entry, described below.
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.El
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.Pp
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The following five members are only valid for entries forming part of
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a user process's address space:
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.Bl -tag -width ".Va max_protection"
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.It Va protection
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Memory protection bits applied to this region.
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.It Va max_protection
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Mask for the memory protection bits which may be actually be applied to
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this region.
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.It Va inheritance
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Contains flags which specify how this entry should be treated
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during fork processing.
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.It Va wired_count
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Count of how many times this entry has been wired into physical memory.
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.It Va lastr
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Contains the address of the last read which caused a page fault.
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.El
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.Pp
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The following flags may be applied to each entry, by specifying them
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as a mask within the
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.Va eflags
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member:
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.Bl -tag -width ".Dv MAP_ENTRY_BEHAV_SEQUENTIAL"
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.It Dv MAP_ENTRY_NOSYNC
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The system should not flush the data associated with this map
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periodically, but only when it needs to.
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.It Dv MAP_ENTRY_IS_SUB_MAP
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If set, then the
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.Va object
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member specifies a subordinate map.
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.It Dv MAP_ENTRY_COW
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Indicate that this is a copy-on-write region.
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.It Dv MAP_ENTRY_NEEDS_COPY
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Indicate that a copy-on-write region needs to be copied.
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.It Dv MAP_ENTRY_NOFAULT
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Specifies that accesses within this region should never cause a page fault.
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If a page fault occurs within this region, the system will panic.
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.It Dv MAP_ENTRY_USER_WIRED
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Indicate that this region was wired on behalf of a user process.
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.It Dv MAP_ENTRY_BEHAV_NORMAL
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The system should use the default paging behaviour for this region.
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.It Dv MAP_ENTRY_BEHAV_SEQUENTIAL
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The system should depress the priority of pages immediately preceding
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each page within this region when faulted in.
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.It Dv MAP_ENTRY_BEHAV_RANDOM
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Is a hint that pages within this region will be accessed randomly,
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and that prefetching is likely not advantageous.
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.It Dv MAP_ENTRY_IN_TRANSITION
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Indicate that wiring or unwiring of an entry is in progress, and that
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other kernel threads should not attempt to modify fields in the structure.
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.It Dv MAP_ENTRY_NEEDS_WAKEUP
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Indicate that there are kernel threads waiting for this region to become
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available.
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.It Dv MAP_ENTRY_NOCOREDUMP
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The region should not be included in a core dump.
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.El
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.Pp
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The
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.Va inheritance
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member has type
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.Vt vm_inherit_t .
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This governs the inheritance behaviour for a map entry during fork processing.
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The following values are defined for
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.Vt vm_inherit_t :
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.Bl -tag -width ".Dv VM_INHERIT_DEFAULT"
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.It Dv VM_INHERIT_SHARE
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The object associated with the entry should be cloned and shared
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with the new map.
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A new
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.Vt struct vm_object
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will be created if necessary.
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.It Dv VM_INHERIT_COPY
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The object associated with the entry should be copied to the new map.
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.It Dv VM_INHERIT_NONE
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The entry should not be copied to the new map.
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.It Dv VM_INHERIT_DEFAULT
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Specifies the default behaviour,
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.Dv VM_INHERIT_COPY .
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.El
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.Pp
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The
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.Vt union vm_map_object
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is used to specify the structure which a
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.Vt struct vm_map_entry
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is associated with.
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.Pp
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The fields of
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.Vt union vm_map_object
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are as follows:
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.Bd -literal -offset indent
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union vm_map_object {
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struct vm_object *vm_object;
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struct vm_map *sub_map;
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};
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.Ed
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.Pp
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Normally, the
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.Va sub_map
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member is only used by system maps to indicate that a memory range
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is managed by a subordinate system map.
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Within a user process map, each
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.Vt struct vm_map_entry
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is backed by a
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.Vt struct vm_object .
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.Sh SEE ALSO
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.Xr pmap 9 ,
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.Xr vm_map_check_protection 9 ,
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.Xr vm_map_create 9 ,
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.Xr vm_map_delete 9 ,
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.Xr vm_map_entry_resize_free 9 ,
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.Xr vm_map_find 9 ,
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.Xr vm_map_findspace 9 ,
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.Xr vm_map_inherit 9 ,
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.Xr vm_map_init 9 ,
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.Xr vm_map_insert 9 ,
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.Xr vm_map_lock 9 ,
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.Xr vm_map_lookup 9 ,
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.Xr vm_map_madvise 9 ,
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.Xr vm_map_max 9 ,
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.Xr vm_map_min 9 ,
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.Xr vm_map_pmap 9 ,
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.Xr vm_map_protect 9 ,
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.Xr vm_map_remove 9 ,
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.Xr vm_map_simplify_entry 9 ,
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.Xr vm_map_stack 9 ,
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.Xr vm_map_submap 9 ,
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.Xr vm_map_sync 9 ,
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.Xr vm_map_wire 9
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.Sh AUTHORS
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This manual page was written by
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.An Bruce M Simpson Aq bms@spc.org .
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