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.\"
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26.\" $FreeBSD: head/share/man/man9/zone.9 179880 2008-06-19 18:33:38Z remko $
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26.\" $FreeBSD: head/share/man/man9/zone.9 213910 2010-10-16 04:14:45Z lstewart $ |
27.\"
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28.Dd June 19, 2008
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28.Dd October 9, 2010 |
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 ,
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38.Nm uma_zone_set_max
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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" "u_int16_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 void 63.Fn uma_zone_set_max "uma_zone_t zone" "int nitems"
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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. 156.Pp 157The variations 158.Fn uma_zalloc_arg 159and 160.Fn uma_zfree_arg 161allow to 162specify an argument for the 163.Dv ctor 164and 165.Dv dtor 166functions, respectively. 167.Pp 168Created zones, 169which are empty, 170can be destroyed using 171.Fn uma_zdestroy , 172freeing all memory that was allocated for the zone. 173All items allocated from the zone with 174.Fn uma_zalloc 175must have been freed with 176.Fn uma_zfree 177before. 178.Pp
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173The purpose of
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179The |
180.Fn uma_zone_set_max
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175is to limit the maximum amount of memory that the system can dedicated
176toward the zone specified by the
177.Fa zone
178argument.
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181function limits the number of items 182.Pq and therefore memory 183that can be allocated to 184.Fa zone . |
185The 186.Fa nitems
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181argument gives the upper limit of items in the zone.
182This limits the total number of items in the zone which includes:
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187argument specifies the requested upper limit number of items. 188The effective limit may end up being higher than requested, as the 189implementation will round up to ensure all memory pages allocated to the zone 190are utilised to capacity. 191The limit applies to the total number of items in the zone, which includes |
192allocated items, free items and free items in the per-cpu caches. 193On systems with more than one CPU it may not be possible to allocate 194the specified number of items even when there is no shortage of memory, 195because all of the remaining free items may be in the caches of the 196other CPUs when the limit is hit.
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197.Pp 198The 199.Fn uma_zone_get_max 200function returns the effective upper limit number of items for a zone. 201.Pp 202The 203.Fn uma_zone_get_cur 204function returns the approximate current occupancy of the zone. 205The returned value is approximate because appropriate synchronisation to 206determine an exact value is not performend by the implementation. 207This ensures low overhead at the expense of potentially stale data being used 208in the calculation. |
209.Sh RETURN VALUES 210The 211.Fn uma_zalloc 212function returns a pointer to an item, or 213.Dv NULL 214if the zone ran out of unused items and the allocator was unable to 215enlarge it. 216.Sh SEE ALSO 217.Xr malloc 9 218.Sh HISTORY 219The zone allocator first appeared in 220.Fx 3.0 . 221It was radically changed in 222.Fx 5.0 223to function as a slab allocator. 224.Sh AUTHORS 225.An -nosplit 226The zone allocator was written by 227.An John S. Dyson . 228The zone allocator was rewritten in large parts by 229.An Jeff Roberson Aq jeff@FreeBSD.org 230to function as a slab allocator. 231.Pp 232This manual page was written by 233.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org . 234Changes for UMA by 235.An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org .
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