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.In sys/param.h 41.In 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 67while they are not allocated, 68so structures that will be managed by the zone allocator 69and wish to use the type stable property of zones by leaving some fields 70pre-filled between allocations, must reserve 71two pointers at the very beginning for internal use by the zone 72allocator, as follows: 73.Bd -literal 74struct my_item { 75 struct my_item *z_rsvd1; 76 struct my_item *z_rsvd2; 77 /* rest of structure */ 78}; 79.Ed 80.Pp 81Alternatively they should assume those entries corrupted 82after each allocation. After the first allocation of an item, 83it will have been cleared to zeroes, however subsequent allocations 84will retain the contents as of the last free, with the exception of the 85fields mentioned above. 86.Pp 87Zones are created in one of two fashions, depending how far along the 88boot process is. 89.Pp 90If the VM system is fully initialized, a dynamically allocated zone can 91be created using 92.Fn zinit . 93The 94.Fa name 95argument should be a pointer to a short, descriptive name for the 96zone; it is used for statistics and debugging purposes. 97The 98.Fa size 99and 100.Fa nentries 101are the size of the items held by the zone and the initial size (in 102items) of the zone, respectively. 103The 104.Fa flags 105argument should be set to 106.Dv ZONE_INTERRUPT 107if there is a chance that items may be allocated from the zone in 108interrupt context; note that in this case, the zone will never grow 109larger than 110.Fa nentries 111items. 112In all other cases, 113.Fa flags 114should be set to 0. 115The final argument, 116.Fa zalloc , 117indicates the number of VM pages by which the zone should grow every 118time it fills up. 119.Pp 120If the VM system is not yet fully initialized, the zone allocator 121cannot dynamically allocate VM pages from which to dole out items, so 122the caller needs to provide a static pool of items. 123In this case, the initialization is done in two stages: first, 124.Fn zbootinit 125is called before first use of the zone; later, when the VM system is 126up, the initialization of the zone is completed by calling 127.Fn zinitna . 128.Pp 129The first argument to 130.Fn zbootinit 131is a pointer to a static 132.Vt "struct vm_zone" 133to initialize. 134The second and third are the name of the zone and the size of the 135items it will hold. 136The fourth argument is a pointer to a static array of items from which 137the zone allocator will draw until the zone is fully initialized. 138The 139.Fa nitems 140argument is the number of items in the array. 141.Pp 142The arguments to 143.Fa zinitna 144are the same as for 145.Fa zinit , 146with the addition of a pointer to the zone to initialize, and a 147pointer to a 148.Vt "struct vm_object" 149from which to allocate pages in the 150.Dv ZONE_INTERRUPT 151case. 152.Pp 153To allocate an item from a zone, simply call 154.Fn zalloc 155with a pointer to that zone; it will return a pointer to an item, or 156.Dv NULL 157in the rare case where all items in the zone are in use and the 158allocator is unable to grow the zone. 159.Pp 160Items are released back to the zone from which they were allocated by 161calling 162.Fn zfree 163with a pointer to the zone and a pointer to the item. 164.Pp 165Zones created with 166.Fn zinit 167or 168.Fn zinitna 169can be destroyed using 170.Fn zdestroy , 171freeing all memory that was allocated for the zone. 172All items allocated from the zone with 173.Fn zalloc 174must have been freed with 175.Fn zfree 176before. 177.Sh RETURN VALUES 178The 179.Fn zinitna 180function returns 1 on success and 0 on failure; the only failure case 181is inability to preallocate address space for an interrupt-safe zone. 182.Pp 183The 184.Fn zinit 185function returns a pointer to a fully initialized 186.Vt "struct vm_zone" , 187or 188.Dv NULL 189if it was unable to 190.Fn malloc 191a 192.Vt "struct vm_zone" 193or the 194.Dv ZONE_INTERRUPT 195flag was specified and 196.Fn zinitna 197failed to preallocate address space. 198.Pp 199The 200.Fn zalloc 201function returns a pointer to an item, or 202.Dv NULL 203if the zone ran out of unused items and the allocator was unable to 204enlarge it. 205.Sh SEE ALSO 206.Xr malloc 9 207.Sh HISTORY 208The zone allocator first appeared in 209.Fx 3.0 . 210.Sh AUTHORS 211.An -nosplit 212The zone allocator was written by 213.An John S. Dyson . 214.Pp 215This manual page was written by 216.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org . 217