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 October 2, 2006 29.Dt ZONE 9 30.Os 31.Sh NAME 32.Nm uma_zcreate , 33.Nm uma_zalloc , 34.Nm uma_zfree , 35.Nm uma_zdestroy , 36.Nm uma_zone_set_max 37.Nd zone allocator 38.Sh SYNOPSIS 39.In sys/param.h 40.In sys/queue.h 41.In vm/uma.h 42.Ft uma_zone_t 43.Fo uma_zcreate 44.Fa "char *name" "int size" 45.Fa "uma_ctor ctor" "uma_dtor dtor" "uma_init uminit" "uma_fini fini" 46.Fa "int align" "u_int16_t flags" 47.Fc 48.Ft "void *" 49.Fn uma_zalloc "uma_zone_t zone" "int flags" 50.Ft void 51.Fn uma_zfree "uma_zone_t zone" "void *item" 52.Ft void 53.Fn uma_zdestroy "uma_zone_t zone" 54.Ft void 55.Fn uma_zone_set_max "uma_zone_t zone" "int nitems" 56.Sh DESCRIPTION 57The zone allocator provides an efficient interface for managing 58dynamically-sized collections of items of similar size. 59The zone allocator can work with preallocated zones as well as with 60runtime-allocated ones, and is therefore available much earlier in the 61boot process than other memory management routines. 62.Pp 63A zone is an extensible collection of items of identical size. 64The zone allocator keeps track of which items are in use and which 65are not, and provides functions for allocating items from the zone and 66for releasing them back (which makes them available for later use). 67.Pp 68After the first allocation of an item, 69it will have been cleared to zeroes, however subsequent allocations 70will retain the contents as of the last free. 71.Pp 72The 73.Fn uma_zcreate 74function creates a new zone from which items may then be allocated from. 75The 76.Fa name 77argument is a text name of the zone for debugging and stats; this memory 78should not be freed until the zone has been deallocated. 79.Pp 80The 81.Fa ctor 82and 83.Fa dtor 84arguments are callback functions that are called by 85the uma subsystem at the time of the call to 86.Fn uma_zalloc 87and 88.Fn uma_zfree 89respectively. 90Their purpose is to provide hooks for initializing or 91destroying things that need to be done at the time of the allocation 92or release of a resource. 93A good usage for the 94.Fa ctor 95and 96.Fa dtor 97callbacks 98might be to adjust a global count of the number of objects allocated. 99.Pp 100The 101.Fa uminit 102and 103.Fa fini 104arguments are used to optimize the allocation of 105objects from the zone. 106They are called by the uma subsystem whenever 107it needs to allocate or free several items to satisfy requests or memory 108pressure. 109A good use for the 110.Fa uminit 111and 112.Fa fini 113callbacks might be to 114initialize and destroy mutexes contained within the object. 115This would 116allow one to re-use already initialized mutexes when an object is returned 117from the uma subsystem's object cache. 118They are not called on each call to 119.Fn uma_zalloc 120and 121.Fn uma_zfree 122but rather in a batch mode on several objects. 123.Pp 124To allocate an item from a zone, simply call 125.Fn uma_zalloc 126with a pointer to that zone 127and set the 128.Fa flags 129argument to selected flags as documented in 130.Xr malloc 9 . 131It will return a pointer to an item if successful, 132or 133.Dv NULL 134in the rare case where all items in the zone are in use and the 135allocator is unable to grow the zone 136or when 137.Dv M_NOWAIT 138is specified. 139.Pp 140Items are released back to the zone from which they were allocated by 141calling 142.Fn uma_zfree 143with a pointer to the zone and a pointer to the item. 144.Pp 145Created zones, 146which are empty, 147can be destroyed using 148.Fn uma_zdestroy , 149freeing all memory that was allocated for the zone. 150All items allocated from the zone with 151.Fn uma_zalloc 152must have been freed with 153.Fn uma_zfree 154before. 155.Pp 156The purpose of 157.Fn uma_zone_set_max 158is to limit the maximum amount of memory that the system can dedicated 159toward the zone specified by the 160.Fa zone 161argument. 162The 163.Fa nitems 164argument gives the upper limit of items in the zone. 165This limits the total number of items in the zone which includes: 166allocated items, free items and free items in the per-cpu caches. 167On systems with more than one CPU it may not be possible to allocate 168the specified number of items even when there is no shortage of memory, 169because all of the remaining free items may be in the caches of the 170other CPUs when the limit is hit. 171.Sh RETURN VALUES 172The 173.Fn uma_zalloc 174function returns a pointer to an item, or 175.Dv NULL 176if the zone ran out of unused items and the allocator was unable to 177enlarge it. 178.Sh SEE ALSO 179.Xr malloc 9 180.Sh HISTORY 181The zone allocator first appeared in 182.Fx 3.0 . 183It was radically changed in 184.Fx 5.0 185to function as a slab allocator. 186.Sh AUTHORS 187.An -nosplit 188The zone allocator was written by 189.An John S. Dyson . 190The zone allocator was rewritten in large parts by 191.An Jeff Roberson Aq jeff@FreeBSD.org 192to function as a slab allocator. 193.Pp 194This manual page was written by 195.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org . 196Changes for UMA by 197.An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org . 198