1.\"- 2.\" Copyright (c) 2001 Dag-Erling Co�dan Sm�rgrav 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 January 27, 2001 29.Dt ZONE 9 30.Os 31.Sh NAME 32.Nm zbootinit , 33.Nm zinitna , 34.Nm zinit , 35.Nm zalloc , 36.Nm zfree , 37.Nm zdestroy 38.Nd zone allocator 39.Sh SYNOPSIS 40.Fd #include <sys/param.h> 41.Fd #include <vm/vm_zone.h> 42.Ft void 43.Fn zbootinit "vm_zone_t z" "char *name" "int size" "void *item" "int nitems" 44.Ft int 45.Fn zinitna "vm_zone_t z" "struct vm_object *obj" "char *name" "int size" "int nentries" "int flags" "int zalloc" 46.Ft vm_zone_t 47.Fn zinit "char *name" "int size" "int nentries" "int flags" "int zalloc" 48.Ft void * 49.Fn zalloc "vm_zone_t z" 50.Ft void 51.Fn zfree "vm_zone_t z" "void *item" 52.Ft void 53.Fn zdestroy "vm_zone_t z" 54.Sh DESCRIPTION 55The zone allocator provides an efficient interface for managing 56dynamically-sized collections of items of similar size. 57The zone allocator can work with preallocated zones as well as with 58runtime-allocated ones, and is therefore available much earlier in the 59boot process than other memory management routines. 60.Pp 61A zone is an extensible collection of items of identical size. 62The zone allocator keeps track of which items are in use and which 63aren't, and provides functions for allocating items from the zone and 64for releasing them back (which makes them available for later use). 65.Pp 66The zone allocator stores state information inside the items proper, 67so structures that will be managed by the zone allocator must reserve 68two pointers at the very beginning for internal use by the zone 69allocator, as follows: 70.Bd -literal 71struct my_item { 72 struct my_item *z_rsvd1; 73 struct my_item *z_rsvd2; 74 /* rest of structure */ 75}; 76.Ed 77.Pp 78Zones are created in one of two fashions, depending how far along the 79boot process is. 80.Pp 81If the VM system is fully initialized, a dynamically allocated zone can 82be created using 83.Fn zinit . 84The 85.Fa name 86argument should be a pointer to a short, descriptive name for the 87zone; it is used for statistics and debugging purposes. 88The 89.Fa size 90and 91.Fa nentries 92are the size of the items held by the zone and the initial size (in 93items) of the zone, respectively. 94The 95.Fa flags 96argument should be set to 97.Dv ZONE_INTERRUPT 98if there is a chance that items may be allocated from the zone in 99interrupt context; note that in this case, the zone will never grow 100larger than 101.Fa nentries 102items. 103In all other cases, 104.Fa flags 105should be set to 0. 106The final argument, 107.Fa zalloc , 108indicates the number of VM pages by which the zone should grow every 109time it fills up. 110.Pp 111If the VM system is not yet fully initialized, the zone allocator 112cannot dynamically allocate VM pages from which to dole out items, so 113the caller needs to provide a static pool of items. 114In this case, the initialization is done in two stages: first, 115.Fn zbootinit 116is called before first use of the zone; later, when the VM system is 117up, the initialization of the zone is completed by calling 118.Fn zinitna . 119.Pp 120The first argument to 121.Fn zbootinit 122is a pointer to a static 123.Vt "struct vm_zone" 124to initialize. 125The second and third are the name of the zone and the size of the 126items it will hold. 127The fourth argument is a pointer to a static array of items from which 128the zone allocator will draw until the zone is fully initialized. 129The 130.Fa nitems 131argument is the number of items in the array. 132.Pp 133The arguments to 134.Fa zinitna 135are the same as for 136.Fa zinit , 137with the addition of a pointer to the zone to initialize, and a 138pointer to a 139.Vt "struct vm_object" 140from which to allocate pages in the 141.Dv ZONE_INTERRUPT 142case. 143.Pp 144To allocate an item from a zone, simply call 145.Fn zalloc 146with a pointer to that zone; it will return a pointer to an item, or 147.Dv NULL 148in the rare case where all items in the zone are in use and the 149allocator is unable to grow the zone. 150.Pp 151Items are released back to the zone from which they were allocated by 152calling 153.Fn zfree 154with a pointer to the zone and a pointer to the item. 155.Pp 156Zones created with 157.Fn zinit 158or 159.Fn zinitna 160can be destroyed using 161.Fn zdestroy , 162freeing all memory that was allocated for the zone. 163All items allocated from the zone with 164.Fn zalloc 165must have been freed with 166.Fn zfree 167before. 168.Sh RETURN VALUES 169The 170.Fn zinitna 171function returns 1 on success and 0 on failure; the only failure case 172is inability to preallocate address space for an interrupt-safe zone. 173.Pp 174The 175.Fn zinit 176function returns a pointer to a fully initialized 177.Vt "struct vm_zone" , 178or 179.Dv NULL 180if it was unable to 181.Fn malloc 182a 183.Vt "struct vm_zone" 184or the 185.Dv ZONE_INTERRUPT 186flag was specified and 187.Fn zinitna 188failed to preallocate address space. 189.Pp 190The 191.Fn zalloc 192function returns a pointer to an item, or 193.Dv NULL 194if the zone ran out of unused items and the allocator was unable to 195enlarge it. 196.Sh SEE ALSO 197.Xr malloc 9 198.Sh HISTORY 199The zone allocator first appeared in 200.Fx 3.0 . 201.Sh AUTHORS 202.An -nosplit 203The zone allocator was written by 204.An John S. Dyson . 205.Pp 206This manual page was written by 207.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org . 208