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 June 19, 2008 29.Dt ZONE 9 30.Os 31.Sh NAME 32.Nm uma_zcreate , 33.Nm uma_zalloc , 34.Nm uma_zalloc_arg , 35.Nm uma_zfree , 36.Nm uma_zfree_arg , 37.Nm uma_zdestroy , 38.Nm uma_zone_set_max 39.Nd zone allocator 40.Sh SYNOPSIS 41.In sys/param.h 42.In sys/queue.h 43.In vm/uma.h 44.Ft uma_zone_t 45.Fo uma_zcreate 46.Fa "char *name" "int size" 47.Fa "uma_ctor ctor" "uma_dtor dtor" "uma_init uminit" "uma_fini fini" 48.Fa "int align" "u_int16_t flags" 49.Fc 50.Ft "void *" 51.Fn uma_zalloc "uma_zone_t zone" "int flags" 52.Ft "void *" 53.Fn uma_zalloc_arg "uma_zone_t zone" "void *arg" "int flags" 54.Ft void 55.Fn uma_zfree "uma_zone_t zone" "void *item" 56.Ft void 57.Fn uma_zfree_arg "uma_zone_t zone" "void *item" "void *arg" 58.Ft void 59.Fn uma_zdestroy "uma_zone_t zone" 60.Ft void 61.Fn uma_zone_set_max "uma_zone_t zone" "int nitems" 62.Sh DESCRIPTION 63The zone allocator provides an efficient interface for managing 64dynamically-sized collections of items of similar size. 65The zone allocator can work with preallocated zones as well as with 66runtime-allocated ones, and is therefore available much earlier in the 67boot process than other memory management routines. 68.Pp 69A zone is an extensible collection of items of identical size. 70The zone allocator keeps track of which items are in use and which 71are not, and provides functions for allocating items from the zone and 72for releasing them back (which makes them available for later use). 73.Pp 74After the first allocation of an item, 75it will have been cleared to zeroes, however subsequent allocations 76will retain the contents as of the last free. 77.Pp 78The 79.Fn uma_zcreate 80function creates a new zone from which items may then be allocated from. 81The 82.Fa name 83argument is a text name of the zone for debugging and stats; this memory 84should not be freed until the zone has been deallocated. 85.Pp 86The 87.Fa ctor 88and 89.Fa dtor 90arguments are callback functions that are called by 91the uma subsystem at the time of the call to 92.Fn uma_zalloc 93and 94.Fn uma_zfree 95respectively. 96Their purpose is to provide hooks for initializing or 97destroying things that need to be done at the time of the allocation 98or release of a resource. 99A good usage for the 100.Fa ctor 101and 102.Fa dtor 103callbacks 104might be to adjust a global count of the number of objects allocated. 105.Pp 106The 107.Fa uminit 108and 109.Fa fini 110arguments are used to optimize the allocation of 111objects from the zone. 112They are called by the uma subsystem whenever 113it needs to allocate or free several items to satisfy requests or memory 114pressure. 115A good use for the 116.Fa uminit 117and 118.Fa fini 119callbacks might be to 120initialize and destroy mutexes contained within the object. 121This would 122allow one to re-use already initialized mutexes when an object is returned 123from the uma subsystem's object cache. 124They are not called on each call to 125.Fn uma_zalloc 126and 127.Fn uma_zfree 128but rather in a batch mode on several objects. 129.Pp 130To allocate an item from a zone, simply call 131.Fn uma_zalloc 132with a pointer to that zone 133and set the 134.Fa flags 135argument to selected flags as documented in 136.Xr malloc 9 . 137It will return a pointer to an item if successful, 138or 139.Dv NULL 140in the rare case where all items in the zone are in use and the 141allocator is unable to grow the zone 142or when 143.Dv M_NOWAIT 144is specified. 145.Pp 146Items are released back to the zone from which they were allocated by 147calling 148.Fn uma_zfree 149with a pointer to the zone and a pointer to the item. 150.Pp 151The variations 152.Fn uma_zalloc_arg 153and 154.Fn uma_zfree_arg 155allow to 156specify an argument for the 157.Dv ctor 158and 159.Dv dtor 160functions, respectively. 161.Pp 162Created zones, 163which are empty, 164can be destroyed using 165.Fn uma_zdestroy , 166freeing all memory that was allocated for the zone. 167All items allocated from the zone with 168.Fn uma_zalloc 169must have been freed with 170.Fn uma_zfree 171before. 172.Pp 173The purpose of 174.Fn uma_zone_set_max 175is to limit the maximum amount of memory that the system can dedicated 176toward the zone specified by the 177.Fa zone 178argument. 179The 180.Fa nitems 181argument gives the upper limit of items in the zone. 182This limits the total number of items in the zone which includes: 183allocated items, free items and free items in the per-cpu caches. 184On systems with more than one CPU it may not be possible to allocate 185the specified number of items even when there is no shortage of memory, 186because all of the remaining free items may be in the caches of the 187other CPUs when the limit is hit. 188.Sh RETURN VALUES 189The 190.Fn uma_zalloc 191function returns a pointer to an item, or 192.Dv NULL 193if the zone ran out of unused items and the allocator was unable to 194enlarge it. 195.Sh SEE ALSO 196.Xr malloc 9 197.Sh HISTORY 198The zone allocator first appeared in 199.Fx 3.0 . 200It was radically changed in 201.Fx 5.0 202to function as a slab allocator. 203.Sh AUTHORS 204.An -nosplit 205The zone allocator was written by 206.An John S. Dyson . 207The zone allocator was rewritten in large parts by 208.An Jeff Roberson Aq jeff@FreeBSD.org 209to function as a slab allocator. 210.Pp 211This manual page was written by 212.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org . 213Changes for UMA by 214.An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org . 215