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