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: src/share/man/man9/zone.9,v 1.9.2.4 2002/05/02 20:01:29 asmodai Exp $ 27.\" $DragonFly: src/share/man/man9/zone.9,v 1.7 2008/01/22 19:17:38 swildner Exp $ 28.\" 29.Dd January 27, 2001 30.Dt ZONE 9 31.Os 32.Sh NAME 33.Nm zbootinit , 34.Nm zinitna , 35.Nm zinit , 36.Nm zdestroy , 37.Nm zalloc , 38.Nm zfree , 39.Nd zone allocator 40.Sh SYNOPSIS 41.In sys/param.h 42.In sys/queue.h 43.In vm/vm_zone.h 44.Ft void 45.Fn zbootinit "vm_zone_t z" "char *name" "int size" "void *item" "int nitems" 46.Ft int 47.Fn zinitna "vm_zone_t z" "struct vm_object *obj" "char *name" "int size" "int nentries" "int flags" "int zalloc" 48.Ft vm_zone_t 49.Fn zinit "char *name" "int size" "int nentries" "int flags" "int zalloc" 50.Ft void 51.Fn zdestroy "vm_zone_t z" 52.Ft void * 53.Fn zalloc "vm_zone_t z" 54.Ft void 55.Fn zfree "vm_zone_t z" "void *item" 56.Sh DESCRIPTION 57The zone allocator is deprecated. 58Use 59.In sys/objcache.h 60for new developments. 61.Pp 62The zone allocator provides an efficient interface for managing 63dynamically-sized collections of items of similar size. 64The zone allocator can work with preallocated zones as well as with 65runtime-allocated ones, and is therefore available much earlier in the 66boot process than other memory management routines. 67.Pp 68A zone is an extensible collection of items of identical size. 69The zone allocator keeps track of which items are in use and which 70are not, and provides functions for allocating items from the zone and 71for releasing them back (which makes them available for later use). 72.Pp 73The zone allocator stores state information inside the items proper 74while they are not allocated, 75so structures that will be managed by the zone allocator 76and wish to use the type stable property of zones by leaving some fields 77pre-filled between allocations, must reserve 78two pointers at the very beginning for internal use by the zone 79allocator, as follows: 80.Bd -literal 81struct my_item { 82 struct my_item *z_rsvd1; 83 struct my_item *z_rsvd2; 84 /* rest of structure */ 85}; 86.Ed 87.Pp 88Alternatively they should assume those entries corrupted 89after each allocation. 90After the first allocation of an item, 91it will have been cleared to zeroes, however subsequent allocations 92will retain the contents as of the last free, with the exception of the 93fields mentioned above. 94.Pp 95Zones are created in one of two fashions, depending how far along the 96boot process is. 97.Pp 98If the VM system is fully initialized, a dynamically allocated zone can 99be created using 100.Fn zinit . 101The 102.Fa name 103argument should be a pointer to a short, descriptive name for the 104zone; it is used for statistics and debugging purposes. 105The 106.Fa size 107and 108.Fa nentries 109are the size of the items held by the zone and the initial size (in 110items) of the zone, respectively. 111The 112.Fa flags 113argument should have the 114.Dv ZONE_INTERRUPT 115bit set if there is a chance that items may be allocated from the zone in 116interrupt context; note that in this case, the zone will never grow 117larger than 118.Fa nentries 119items. 120The 121.Fa flags 122argument should have the 123.Dv ZONE_DESTROYABLE 124bit set if the zone is to be destroyed with 125.Fn zdestroy . 126The final argument, 127.Fa zalloc , 128indicates the number of VM pages by which the zone should grow every 129time it fills up. 130.Pp 131If the VM system is not yet fully initialized, the zone allocator 132cannot dynamically allocate VM pages from which to dole out items, so 133the caller needs to provide a static pool of items. 134In this case, the initialization is done in two stages: first, 135.Fn zbootinit 136is called before first use of the zone; later, when the VM system is 137up, the initialization of the zone is completed by calling 138.Fn zinitna . 139.Pp 140The first argument to 141.Fn zbootinit 142is a pointer to a static 143.Vt "struct vm_zone" 144to initialize. 145The second and third are the name of the zone and the size of the 146items it will hold. 147The fourth argument is a pointer to a static array of items from which 148the zone allocator will draw until the zone is fully initialized. 149The 150.Fa nitems 151argument is the number of items in the array. 152.Pp 153The arguments to 154.Fa zinitna 155are the same as for 156.Fa zinit , 157with the addition of a pointer to the zone to initialize, and a 158pointer to a 159.Vt "struct vm_object" 160from which to allocate pages in the 161.Dv ZONE_INTERRUPT 162case. 163.Pp 164To release all the memory allocated for a zone, call 165.Fn zdestroy . 166Only zones created with 167.Fn zinit 168and with the 169.Dv ZONE_DESTROYABLE 170flag can be destroyed. 171.Pp 172To allocate an item from a zone, simply call 173.Fn zalloc 174with a pointer to that zone; it will return a pointer to an item, or 175.Dv NULL 176in the rare case where all items in the zone are in use and the 177allocator is unable to grow the zone. 178.Pp 179Items are released back to the zone from which they were allocated by 180calling 181.Fn zfree 182with a pointer to the zone and a pointer to the item. 183.Pp 184The zone functions are not SMP-safe. 185The MP lock must be held while calling them. 186.Sh RETURN VALUES 187The 188.Fn zinitna 189function returns 1 on success and 0 on failure; the only failure case 190is inability to preallocate address space for an interrupt-safe zone. 191.Pp 192The 193.Fn zinit 194function returns a pointer to a fully initialized 195.Vt "struct vm_zone" , 196or 197.Dv NULL 198if it was unable to 199.Fn kmalloc 200a 201.Vt "struct vm_zone" 202or the 203.Dv ZONE_INTERRUPT 204flag was specified and 205.Fn zinitna 206failed to preallocate address space. 207.Pp 208The 209.Fn zalloc 210function returns a pointer to an item, or 211.Dv NULL 212if the zone ran out of unused items and the allocator was unable to 213enlarge it. 214.Sh SEE ALSO 215.Xr memory 9 216.Sh HISTORY 217The zone allocator first appeared in 218.Fx 3.0 . 219.Sh AUTHORS 220.An -nosplit 221The zone allocator was written by 222.An John S. Dyson . 223.Pp 224This manual page was written by 225.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org . 226