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1.\"- 2.\" Copyright (c) 2001 Dag-Erling CoĂŻdan SmĂ¸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 February 25, 2012 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.Nm uma_zone_get_max, 40.Nm uma_zone_get_cur 41.Nd zone allocator 42.Sh SYNOPSIS 43.In sys/param.h 44.In sys/queue.h 45.In vm/uma.h 46.Ft uma_zone_t 47.Fo uma_zcreate 48.Fa "char *name" "int size" 49.Fa "uma_ctor ctor" "uma_dtor dtor" "uma_init uminit" "uma_fini fini" 50.Fa "int align" "uint16_t flags" 51.Fc 52.Ft "void *" 53.Fn uma_zalloc "uma_zone_t zone" "int flags" 54.Ft "void *" 55.Fn uma_zalloc_arg "uma_zone_t zone" "void *arg" "int flags" 56.Ft void 57.Fn uma_zfree "uma_zone_t zone" "void *item" 58.Ft void 59.Fn uma_zfree_arg "uma_zone_t zone" "void *item" "void *arg" 60.Ft void 61.Fn uma_zdestroy "uma_zone_t zone" 62.Ft int 63.Fn uma_zone_set_max "uma_zone_t zone" "int nitems" 64.Ft int 65.Fn uma_zone_get_max "uma_zone_t zone" 66.Ft int 67.Fn uma_zone_get_cur "uma_zone_t zone" 68.Sh DESCRIPTION 69The zone allocator provides an efficient interface for managing 70dynamically-sized collections of items of similar size. 71The zone allocator can work with preallocated zones as well as with 72runtime-allocated ones, and is therefore available much earlier in the 73boot process than other memory management routines. 74.Pp 75A zone is an extensible collection of items of identical size. 76The zone allocator keeps track of which items are in use and which 77are not, and provides functions for allocating items from the zone and 78for releasing them back (which makes them available for later use). 79.Pp 80After the first allocation of an item, 81it will have been cleared to zeroes, however subsequent allocations 82will retain the contents as of the last free. 83.Pp 84The 85.Fn uma_zcreate 86function creates a new zone from which items may then be allocated from. 87The 88.Fa name 89argument is a text name of the zone for debugging and stats; this memory 90should not be freed until the zone has been deallocated. 91.Pp 92The 93.Fa ctor 94and 95.Fa dtor 96arguments are callback functions that are called by 97the uma subsystem at the time of the call to 98.Fn uma_zalloc 99and 100.Fn uma_zfree 101respectively. 102Their purpose is to provide hooks for initializing or 103destroying things that need to be done at the time of the allocation 104or release of a resource. 105A good usage for the 106.Fa ctor 107and 108.Fa dtor 109callbacks 110might be to adjust a global count of the number of objects allocated. 111.Pp 112The 113.Fa uminit 114and 115.Fa fini 116arguments are used to optimize the allocation of 117objects from the zone. 118They are called by the uma subsystem whenever 119it needs to allocate or free several items to satisfy requests or memory 120pressure. 121A good use for the 122.Fa uminit 123and 124.Fa fini 125callbacks might be to 126initialize and destroy mutexes contained within the object. 127This would 128allow one to re-use already initialized mutexes when an object is returned 129from the uma subsystem's object cache. 130They are not called on each call to 131.Fn uma_zalloc 132and 133.Fn uma_zfree 134but rather in a batch mode on several objects. 135.Pp 136To allocate an item from a zone, simply call 137.Fn uma_zalloc 138with a pointer to that zone 139and set the 140.Fa flags 141argument to selected flags as documented in 142.Xr malloc 9 . 143It will return a pointer to an item if successful, 144or 145.Dv NULL 146in the rare case where all items in the zone are in use and the 147allocator is unable to grow the zone 148or when 149.Dv M_NOWAIT 150is specified. 151.Pp 152Items are released back to the zone from which they were allocated by 153calling 154.Fn uma_zfree 155with a pointer to the zone and a pointer to the item. 156If 157.Fa item 158is 159.Dv NULL , 160then 161.Fn uma_zfree 162does nothing. 163.Pp 164The variations 165.Fn uma_zalloc_arg 166and 167.Fn uma_zfree_arg 168allow to 169specify an argument for the 170.Dv ctor 171and 172.Dv dtor 173functions, respectively. 174.Pp 175Created zones, 176which are empty, 177can be destroyed using 178.Fn uma_zdestroy , 179freeing all memory that was allocated for the zone. 180All items allocated from the zone with 181.Fn uma_zalloc 182must have been freed with 183.Fn uma_zfree 184before. 185.Pp 186The 187.Fn uma_zone_set_max 188function limits the number of items 189.Pq and therefore memory 190that can be allocated to 191.Fa zone . 192The 193.Fa nitems 194argument specifies the requested upper limit number of items. 195The effective limit is returned to the caller, as it may end up being higher 196than requested due to the implementation rounding up to ensure all memory pages 197allocated to the zone are utilised to capacity. 198The limit applies to the total number of items in the zone, which includes 199allocated items, free items and free items in the per-cpu caches. 200On systems with more than one CPU it may not be possible to allocate 201the specified number of items even when there is no shortage of memory, 202because all of the remaining free items may be in the caches of the 203other CPUs when the limit is hit. 204.Pp 205The 206.Fn uma_zone_get_max 207function returns the effective upper limit number of items for a zone. 208.Pp 209The 210.Fn uma_zone_get_cur 211function returns the approximate current occupancy of the zone. 212The returned value is approximate because appropriate synchronisation to 213determine an exact value is not performed by the implementation. 214This ensures low overhead at the expense of potentially stale data being used 215in the calculation. 216.Sh RETURN VALUES 217The 218.Fn uma_zalloc 219function returns a pointer to an item, or 220.Dv NULL 221if the zone ran out of unused items and the allocator was unable to 222enlarge it. 223.Sh SEE ALSO 224.Xr malloc 9 225.Sh HISTORY 226The zone allocator first appeared in 227.Fx 3.0 . 228It was radically changed in 229.Fx 5.0 230to function as a slab allocator. 231.Sh AUTHORS 232.An -nosplit 233The zone allocator was written by 234.An John S. Dyson . 235The zone allocator was rewritten in large parts by 236.An Jeff Roberson Aq jeff@FreeBSD.org 237to function as a slab allocator. 238.Pp 239This manual page was written by 240.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org . 241Changes for UMA by 242.An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org .