1.\" 2.\" Copyright (c) 2003 Bruce M Simpson <bms@spc.org> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd July 19, 2003 29.Dt VM_MAP 9 30.Os 31.Sh NAME 32.Nm vm_map 33.Nd virtual address space portion of virtual memory subsystem 34.Sh SYNOPSIS 35.In sys/param.h 36.In vm/vm.h 37.In vm/vm_map.h 38.Sh DESCRIPTION 39The 40.Nm 41subsystem is used to manage virtual address spaces. 42This section describes the main data structures used within the code. 43.Pp 44The 45.Vt "struct vm_map" 46is a generic representation of an address space. 47This address space may belong to a user process or the kernel. 48The kernel actually uses several maps, which are maintained as 49subordinate maps, created using the 50.Xr vm_map_submap 9 51function. 52.Bd -literal -offset indent 53struct vm_map { 54 struct vm_map_entry header; 55 struct sx lock; 56 struct mtx system_mtx; 57 int nentries; 58 vm_size_t size; 59 u_int timestamp; 60 u_char needs_wakeup; 61 u_char system_map; 62 vm_flags_t flags; 63 vm_map_entry_t root; 64 pmap_t pmap; 65#define min_offset header.start 66#define max_offset header.end 67}; 68.Ed 69.Pp 70The fields of 71.Vt struct vm_map 72are as follows: 73.Bl -tag -width ".Va needs_wakeup" 74.It Va header 75Head node of a circular, doubly linked list of 76.Vt struct vm_map_entry 77objects. 78Each object defines a particular region within this map's address space. 79.It Va lock 80Used to serialize access to the structure. 81.It Va system_mtx 82A mutex which is used if the map is a system map. 83.It Va nentries 84A count of the members in use within the circular map entry list. 85.It Va size 86Specifies the size of the virtual address space. 87.It Va timestamp 88Used to determine if the map has changed since its last access. 89.It Va needs_wakeup 90Indicates if a thread is waiting for an allocation within the map. 91Used only by system maps. 92.It Va system_map 93Set to TRUE to indicate that map is a system map; otherwise, it belongs 94to a user process. 95.It Va flags 96Map flags. 97.It Va root 98Root node of a binary search tree used for fast lookup of map entries. 99.It Va pmap 100Pointer to the underlying physical map with which this virtual map 101is associated. 102.It Va min_offset 103The minimum 104.Va vm_offset_t 105in this map. 106Programs should never use 107.Va header.start 108or 109.Va header.end 110directly, use 111.Va min_offset 112and 113.Va max_offset 114instead. 115.It Va max_offset 116The maximum 117.Va vm_offset_t 118in this map. 119.El 120.Pp 121The following flags can be passed to 122.Xr vm_map_find 9 123and 124.Xr vm_map_insert 9 125to specify the copy-on-write properties of regions within the map: 126.Bl -tag -width ".Dv MAP_PREFAULT_MADVISE" 127.It Dv MAP_COPY_ON_WRITE 128The mapping is copy-on-write. 129.It Dv MAP_NOFAULT 130The mapping should not generate page faults. 131.It Dv MAP_PREFAULT 132The mapping should be prefaulted into physical memory. 133.It Dv MAP_PREFAULT_PARTIAL 134The mapping should be partially prefaulted into physical memory. 135.It Dv MAP_DISABLE_SYNCER 136Do not periodically flush dirty pages; only flush them when absolutely 137necessary. 138.It Dv MAP_DISABLE_COREDUMP 139Do not include the mapping in a core dump. 140.It Dv MAP_PREFAULT_MADVISE 141Specify that the request from a user process calling 142.Xr madvise 2 . 143.El 144.Pp 145The 146.Vt struct vm_map_entry 147is a generic representation of a region. 148The region managed by each entry is associated with a 149.Vt union vm_map_object , 150described below. 151.Bd -literal -offset indent 152struct vm_map_entry { 153 struct vm_map_entry *prev; 154 struct vm_map_entry *next; 155 struct vm_map_entry *left; 156 struct vm_map_entry *right; 157 vm_offset_t start; 158 vm_offset_t end; 159 vm_offset_t avail_ssize; 160 vm_size_t adj_free; 161 vm_size_t max_free; 162 union vm_map_object object; 163 vm_ooffset_t offset; 164 vm_eflags_t eflags; 165 /* Only in task maps: */ 166 vm_prot_t protection; 167 vm_prot_t max_protection; 168 vm_inherit_t inheritance; 169 int wired_count; 170 vm_pindex_t lastr; 171}; 172.Ed 173.Pp 174The fields of 175.Vt struct vm_map_entry 176are as follows: 177.Bl -tag -width ".Va avail_ssize" 178.It Va prev 179Pointer to the previous node in a doubly-linked, circular list. 180.It Va next 181Pointer to the next node in a doubly-linked, circular list. 182.It Va left 183Pointer to the left node in a binary search tree. 184.It Va right 185Pointer to the right node in a binary search tree. 186.It Va start 187Lower address bound of this entry's region. 188.It Va end 189Upper address bound of this entry's region. 190.It Va avail_ssize 191If the entry is for a process stack, specifies how much the entry can grow. 192.It Va adj_free 193The amount of free, unmapped address space adjacent to and immediately 194following this map entry. 195.It Va max_free 196The maximum amount of contiguous free space in this map entry's subtree. 197.It Va object 198Pointer to the 199.Vt struct vm_map_object 200with which this entry is associated. 201.It Va offset 202Offset within the 203.Va object 204which is mapped from 205.Va start 206onwards. 207.It Va eflags 208Flags applied to this entry, described below. 209.El 210.Pp 211The following five members are only valid for entries forming part of 212a user process's address space: 213.Bl -tag -width ".Va max_protection" 214.It Va protection 215Memory protection bits applied to this region. 216These are identical to those defined for 217.Xr vm_page_protect 9 . 218.It Va max_protection 219Mask for the memory protection bits which may be actually be applied to 220this region. 221These are identical to those defined for 222.Xr vm_page_protect 9 . 223.It Va inheritance 224Contains flags which specify how this entry should be treated 225during fork processing. 226.It Va wired_count 227Count of how many times this entry has been wired into physical memory. 228.It Va lastr 229Contains the address of the last read which caused a page fault. 230.El 231.Pp 232The following flags may be applied to each entry, by specifying them 233as a mask within the 234.Va eflags 235member: 236.Bl -tag -width ".Dv MAP_ENTRY_BEHAV_SEQUENTIAL" 237.It Dv MAP_ENTRY_NOSYNC 238The system should not flush the data associated with this map 239periodically, but only when it needs to. 240.It Dv MAP_ENTRY_IS_SUB_MAP 241If set, then the 242.Va object 243member specifies a subordinate map. 244.It Dv MAP_ENTRY_COW 245Indicate that this is a copy-on-write region. 246.It Dv MAP_ENTRY_NEEDS_COPY 247Indicate that a copy-on-write region needs to be copied. 248.It Dv MAP_ENTRY_NOFAULT 249Specifies that accesses within this region should never cause a page fault. 250If a page fault occurs within this region, the system will panic. 251.It Dv MAP_ENTRY_USER_WIRED 252Indicate that this region was wired on behalf of a user process. 253.It Dv MAP_ENTRY_BEHAV_NORMAL 254The system should use the default paging behaviour for this region. 255.It Dv MAP_ENTRY_BEHAV_SEQUENTIAL 256The system should depress the priority of pages immediately preceding 257each page within this region when faulted in. 258.It Dv MAP_ENTRY_BEHAV_RANDOM 259Is a hint that pages within this region will be accessed randomly, 260and that prefetching is likely not advantageous. 261.It Dv MAP_ENTRY_IN_TRANSITION 262Indicate that wiring or unwiring of an entry is in progress, and that 263other kernel threads should not attempt to modify fields in the structure. 264.It Dv MAP_ENTRY_NEEDS_WAKEUP 265Indicate that there are kernel threads waiting for this region to become 266available. 267.It Dv MAP_ENTRY_NOCOREDUMP 268The region should not be included in a core dump. 269.El 270.Pp 271The 272.Va inheritance 273member has type 274.Vt vm_inherit_t . 275This governs the inheritance behaviour for a map entry during fork processing. 276The following values are defined for 277.Vt vm_inherit_t : 278.Bl -tag -width ".Dv VM_INHERIT_DEFAULT" 279.It Dv VM_INHERIT_SHARE 280The object associated with the entry should be cloned and shared 281with the new map. 282A new 283.Vt struct vm_object 284will be created if necessary. 285.It Dv VM_INHERIT_COPY 286The object associated with the entry should be copied to the new map. 287.It Dv VM_INHERIT_NONE 288The entry should not be copied to the new map. 289.It Dv VM_INHERIT_DEFAULT 290Specifies the default behaviour, 291.Dv VM_INHERIT_COPY . 292.El 293.Pp 294The 295.Vt union vm_map_object 296is used to specify the structure which a 297.Vt struct vm_map_entry 298is associated with. 299.Pp 300The fields of 301.Vt union vm_map_object 302are as follows: 303.Bd -literal -offset indent 304union vm_map_object { 305 struct vm_object *vm_object; 306 struct vm_map *sub_map; 307}; 308.Pp 309.Ed 310Normally, the 311.Va sub_map 312member is only used by system maps to indicate that a memory range 313is managed by a subordinate system map. 314Within a user process map, each 315.Vt struct vm_map_entry 316is backed by a 317.Vt struct vm_object . 318.Sh SEE ALSO 319.Xr pmap 9 , 320.Xr vm_map_check_protection 9 , 321.Xr vm_map_clean 9 , 322.Xr vm_map_create 9 , 323.Xr vm_map_delete 9 , 324.Xr vm_map_find 9 , 325.Xr vm_map_findspace 9 , 326.Xr vm_map_inherit 9 , 327.Xr vm_map_init 9 , 328.Xr vm_map_insert 9 , 329.Xr vm_map_lock 9 , 330.Xr vm_map_lookup 9 , 331.Xr vm_map_madvise 9 , 332.Xr vm_map_max 9 , 333.Xr vm_map_min 9 , 334.Xr vm_map_pmap 9 , 335.Xr vm_map_protect 9 , 336.Xr vm_map_remove 9 , 337.Xr vm_map_simplify_entry 9 , 338.Xr vm_map_stack 9 , 339.Xr vm_map_submap 9 , 340.Xr vm_map_wire 9 , 341.Xr vm_page_protect 9 342.Sh AUTHORS 343This manual page was written by 344.An Bruce M Simpson Aq bms@spc.org . 345