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. 84After the first allocation of an item, 85it will have been cleared to zeroes, however subsequent allocations 86will retain the contents as of the last free, with the exception of the 87fields mentioned above. 88.Pp 89Zones are created in one of two fashions, depending how far along the 90boot process is. 91.Pp 92If the VM system is fully initialized, a dynamically allocated zone can 93be created using 94.Fn zinit . 95The 96.Fa name 97argument should be a pointer to a short, descriptive name for the 98zone; it is used for statistics and debugging purposes. 99The 100.Fa size 101and 102.Fa nentries 103are the size of the items held by the zone and the initial size (in 104items) of the zone, respectively. 105The 106.Fa flags 107argument should be set to 108.Dv ZONE_INTERRUPT 109if there is a chance that items may be allocated from the zone in 110interrupt context; note that in this case, the zone will never grow 111larger than 112.Fa nentries 113items. 114In all other cases, 115.Fa flags 116should be set to 0. 117The final argument, 118.Fa zalloc , 119indicates the number of VM pages by which the zone should grow every 120time it fills up. 121.Pp 122If the VM system is not yet fully initialized, the zone allocator 123cannot dynamically allocate VM pages from which to dole out items, so 124the caller needs to provide a static pool of items. 125In this case, the initialization is done in two stages: first, 126.Fn zbootinit 127is called before first use of the zone; later, when the VM system is 128up, the initialization of the zone is completed by calling 129.Fn zinitna . 130.Pp 131The first argument to 132.Fn zbootinit 133is a pointer to a static 134.Vt "struct vm_zone" 135to initialize. 136The second and third are the name of the zone and the size of the 137items it will hold. 138The fourth argument is a pointer to a static array of items from which 139the zone allocator will draw until the zone is fully initialized. 140The 141.Fa nitems 142argument is the number of items in the array. 143.Pp 144The arguments to 145.Fa zinitna 146are the same as for 147.Fa zinit , 148with the addition of a pointer to the zone to initialize, and a 149pointer to a 150.Vt "struct vm_object" 151from which to allocate pages in the 152.Dv ZONE_INTERRUPT 153case. 154.Pp 155To allocate an item from a zone, simply call 156.Fn zalloc 157with a pointer to that zone; it will return a pointer to an item, or 158.Dv NULL 159in the rare case where all items in the zone are in use and the 160allocator is unable to grow the zone. 161.Pp 162Items are released back to the zone from which they were allocated by 163calling 164.Fn zfree 165with a pointer to the zone and a pointer to the item. 166.Pp 167Zones created with 168.Fn zinit 169or 170.Fn zinitna 171can be destroyed using 172.Fn zdestroy , 173freeing all memory that was allocated for the zone. 174All items allocated from the zone with 175.Fn zalloc 176must have been freed with 177.Fn zfree 178before. 179.Sh RETURN VALUES 180The 181.Fn zinitna 182function returns 1 on success and 0 on failure; the only failure case 183is inability to preallocate address space for an interrupt-safe zone. 184.Pp 185The 186.Fn zinit 187function returns a pointer to a fully initialized 188.Vt "struct vm_zone" , 189or 190.Dv NULL 191if it was unable to 192.Fn malloc 193a 194.Vt "struct vm_zone" 195or the 196.Dv ZONE_INTERRUPT 197flag was specified and 198.Fn zinitna 199failed to preallocate address space. 200.Pp 201The 202.Fn zalloc 203function returns a pointer to an item, or 204.Dv NULL 205if the zone ran out of unused items and the allocator was unable to 206enlarge it. 207.Sh SEE ALSO 208.Xr malloc 9 209.Sh HISTORY 210The zone allocator first appeared in 211.Fx 3.0 . 212.Sh AUTHORS 213.An -nosplit 214The zone allocator was written by 215.An John S. Dyson . 216.Pp 217This manual page was written by 218.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org . 219