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 July 21, 2003 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 68The zone allocator stores state information inside the items proper 69while they are not allocated, 70so structures that will be managed by the zone allocator 71and wish to use the type stable property of zones by leaving some fields 72pre-filled between allocations, must reserve 73two pointers at the very beginning for internal use by the zone 74allocator, as follows: 75.Bd -literal -offset indent 76struct my_item { 77 struct my_item *z_rsvd1; 78 struct my_item *z_rsvd2; 79 /* rest of structure */ 80}; 81.Ed 82.Pp 83Alternatively they should assume those entries corrupted 84after each allocation. 85After the first allocation of an item, 86it will have been cleared to zeroes, however subsequent allocations 87will retain the contents as of the last free, with the exception of the 88fields mentioned above. 89.Pp 90The 91.Fn uma_zcreate 92function creates a new zone from which items may then be allocated from. 93The 94.Fa name 95argument is a text name of the zone for debugging and stats; this memory 96should not be freed until the zone has been deallocated. 97.Pp 98The 99.Fa ctor 100and 101.Fa dtor 102arguments are callback functions that are called by 103the uma subsystem at the time of the call to 104.Fn uma_zalloc 105and 106.Fn uma_zfree 107respectively. 108Their purpose is to provide hooks for initializing or 109destroying things that need to be done at the time of the allocation 110or release of a resource. 111A good usage for the 112.Fa ctor 113and 114.Fa dtor 115callbacks 116might be to adjust a global count of the number of objects allocated. 117.Pp 118The 119.Fa uminit 120and 121.Fa fini 122arguments are used to optimize the allocation of 123objects from the zone. 124They are called by the uma subsystem whenever 125it needs to allocate or free several items to satisfy requests or memory 126pressure. 127A good use for the 128.Fa uminit 129and 130.Fa fini 131callbacks might be to 132initialize and destroy mutexes contained within the object. 133This would 134allow one to re-use already initialized mutexes when an object is returned 135from the uma subsystem's object cache. 136They are not called on each call to 137.Fn uma_zalloc 138and 139.Fn uma_zfree 140but rather in a batch mode on several objects. 141.Pp 142To allocate an item from a zone, simply call 143.Fn uma_zalloc 144with a pointer to that zone 145and set the 146.Fa flags 147argument to selected flags as documented in 148.Xr malloc 9 . 149It will return a pointer to an item if successful, 150or 151.Dv NULL 152in the rare case where all items in the zone are in use and the 153allocator is unable to grow the zone 154or when 155.Dv M_NOWAIT 156is specified. 157.Pp 158Items are released back to the zone from which they were allocated by 159calling 160.Fn uma_zfree 161with a pointer to the zone and a pointer to the item. 162.Pp 163Created zones, 164which are empty, 165can be destroyed using 166.Fn uma_zdestroy , 167freeing all memory that was allocated for the zone. 168All items allocated from the zone with 169.Fn uma_zalloc 170must have been freed with 171.Fn uma_zfree 172before. 173.Pp 174The purpose of 175.Fn uma_zone_set_max 176is to limit the maximum amount of memory that the system can dedicated 177toward the zone specified by the 178.Fa zone 179argument. 180The 181.Fa nitems 182argument gives the upper limit of items in the zone. 183This limits the total number of items in the zone which includes: 184allocated items, free items and free items in the per-cpu caches. 185On systems with more than one CPU it may not be possible to allocate 186the specified number of items even when there is no shortage of memory, 187because all of the remaining free items may be in the caches of the 188other CPUs when the limit is hit. 189.Sh RETURN VALUES 190The 191.Fn uma_zalloc 192function returns a pointer to an item, or 193.Dv NULL 194if the zone ran out of unused items and the allocator was unable to 195enlarge it. 196.Sh SEE ALSO 197.Xr malloc 9 198.Sh HISTORY 199The zone allocator first appeared in 200.Fx 3.0 . 201It was radically changed in 202.Fx 5.0 203to function as a slab allocator. 204.Sh AUTHORS 205.An -nosplit 206The zone allocator was written by 207.An John S. Dyson . 208The zone allocator was rewritten in large parts by 209.An Jeff Roberson Aq jeff@FreeBSD.org 210to function as a slab allocator. 211.Pp 212This manual page was written by 213.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org . 214Changes for UMA by 215.An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org . 216