1.\"- 2.\" Copyright (c) 2001 Dag-Erling Coïdan Smørgrav 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 April 26, 2017 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.Nm uma_zone_set_warning, 42.Nm uma_zone_set_maxaction 43.Nd zone allocator 44.Sh SYNOPSIS 45.In sys/param.h 46.In sys/queue.h 47.In vm/uma.h 48.Ft uma_zone_t 49.Fo uma_zcreate 50.Fa "char *name" "int size" 51.Fa "uma_ctor ctor" "uma_dtor dtor" "uma_init uminit" "uma_fini fini" 52.Fa "int align" "uint16_t flags" 53.Fc 54.Ft "void *" 55.Fn uma_zalloc "uma_zone_t zone" "int flags" 56.Ft "void *" 57.Fn uma_zalloc_arg "uma_zone_t zone" "void *arg" "int flags" 58.Ft void 59.Fn uma_zfree "uma_zone_t zone" "void *item" 60.Ft void 61.Fn uma_zfree_arg "uma_zone_t zone" "void *item" "void *arg" 62.Ft void 63.Fn uma_zdestroy "uma_zone_t zone" 64.Ft int 65.Fn uma_zone_set_max "uma_zone_t zone" "int nitems" 66.Ft int 67.Fn uma_zone_get_max "uma_zone_t zone" 68.Ft int 69.Fn uma_zone_get_cur "uma_zone_t zone" 70.Ft void 71.Fn uma_zone_set_warning "uma_zone_t zone" "const char *warning" 72.Ft void 73.Fn uma_zone_set_maxaction "uma_zone_t zone" "void (*maxaction)(uma_zone_t)" 74.In sys/sysctl.h 75.Fn SYSCTL_UMA_MAX parent nbr name access zone descr 76.Fn SYSCTL_ADD_UMA_MAX ctx parent nbr name access zone descr 77.Fn SYSCTL_UMA_CUR parent nbr name access zone descr 78.Fn SYSCTL_ADD_UMA_CUR ctx parent nbr name access zone descr 79.Sh DESCRIPTION 80The zone allocator provides an efficient interface for managing 81dynamically-sized collections of items of similar size. 82The zone allocator can work with preallocated zones as well as with 83runtime-allocated ones, and is therefore available much earlier in the 84boot process than other memory management routines. 85.Pp 86A zone is an extensible collection of items of identical size. 87The zone allocator keeps track of which items are in use and which 88are not, and provides functions for allocating items from the zone and 89for releasing them back (which makes them available for later use). 90.Pp 91After the first allocation of an item, 92it will have been cleared to zeroes, however subsequent allocations 93will retain the contents as of the last free. 94.Pp 95The 96.Fn uma_zcreate 97function creates a new zone from which items may then be allocated from. 98The 99.Fa name 100argument is a text name of the zone for debugging and stats; this memory 101should not be freed until the zone has been deallocated. 102.Pp 103The 104.Fa ctor 105and 106.Fa dtor 107arguments are callback functions that are called by 108the uma subsystem at the time of the call to 109.Fn uma_zalloc 110and 111.Fn uma_zfree 112respectively. 113Their purpose is to provide hooks for initializing or 114destroying things that need to be done at the time of the allocation 115or release of a resource. 116A good usage for the 117.Fa ctor 118and 119.Fa dtor 120callbacks 121might be to adjust a global count of the number of objects allocated. 122.Pp 123The 124.Fa uminit 125and 126.Fa fini 127arguments are used to optimize the allocation of 128objects from the zone. 129They are called by the uma subsystem whenever 130it needs to allocate or free several items to satisfy requests or memory 131pressure. 132A good use for the 133.Fa uminit 134and 135.Fa fini 136callbacks might be to 137initialize and destroy mutexes contained within the object. 138This would 139allow one to re-use already initialized mutexes when an object is returned 140from the uma subsystem's object cache. 141They are not called on each call to 142.Fn uma_zalloc 143and 144.Fn uma_zfree 145but rather in a batch mode on several objects. 146.Pp 147The 148.Fa flags 149argument of the 150.Fn uma_zcreate 151is a subset of the following flags: 152.Bl -tag -width "foo" 153.It Dv UMA_ZONE_NOFREE 154Slabs of the zone are never returned back to VM. 155.It Dv UMA_ZONE_NODUMP 156Pages belonging to the zone will not be included into mini-dumps. 157.It Dv UMA_ZONE_PCPU 158An allocation from zone would have 159.Va mp_ncpu 160shadow copies, that are privately assigned to CPUs. 161A CPU can address its private copy using base allocation address plus 162multiple of current CPU id and 163.Fn sizeof "struct pcpu" : 164.Bd -literal -offset indent 165foo_zone = uma_zcreate(..., UMA_ZONE_PCPU); 166 ... 167foo_base = uma_zalloc(foo_zone, ...); 168 ... 169critical_enter(); 170foo_pcpu = (foo_t *)zpcpu_get(foo_base); 171/* do something with foo_pcpu */ 172critical_exit(); 173.Ed 174.It Dv UMA_ZONE_OFFPAGE 175By default book-keeping of items within a slab is done in the slab page itself. 176This flag explicitly tells subsystem that book-keeping structure should be 177allocated separately from special internal zone. 178This flag requires either 179.Dv UMA_ZONE_VTOSLAB 180or 181.Dv UMA_ZONE_HASH , 182since subsystem requires a mechanism to find a book-keeping structure 183to an item being freed. 184The subsystem may choose to prefer offpage book-keeping for certain zones 185implicitly. 186.It Dv UMA_ZONE_ZINIT 187The zone will have its 188.Ft uma_init 189method set to internal method that initializes a new allocated slab 190to all zeros. 191Do not mistake 192.Ft uma_init 193method with 194.Ft uma_ctor . 195A zone with 196.Dv UMA_ZONE_ZINIT 197flag would not return zeroed memory on every 198.Fn uma_zalloc . 199.It Dv UMA_ZONE_HASH 200The zone should use an internal hash table to find slab book-keeping 201structure where an allocation being freed belongs to. 202.It Dv UMA_ZONE_VTOSLAB 203The zone should use special field of 204.Vt vm_page_t 205to find slab book-keeping structure where an allocation being freed belongs to. 206.It Dv UMA_ZONE_MALLOC 207The zone is for the 208.Xr malloc 9 209subsystem. 210.It Dv UMA_ZONE_VM 211The zone is for the VM subsystem. 212.El 213.Pp 214To allocate an item from a zone, simply call 215.Fn uma_zalloc 216with a pointer to that zone 217and set the 218.Fa flags 219argument to selected flags as documented in 220.Xr malloc 9 . 221It will return a pointer to an item if successful, 222or 223.Dv NULL 224in the rare case where all items in the zone are in use and the 225allocator is unable to grow the zone 226and 227.Dv M_NOWAIT 228is specified. 229.Pp 230Items are released back to the zone from which they were allocated by 231calling 232.Fn uma_zfree 233with a pointer to the zone and a pointer to the item. 234If 235.Fa item 236is 237.Dv NULL , 238then 239.Fn uma_zfree 240does nothing. 241.Pp 242The variations 243.Fn uma_zalloc_arg 244and 245.Fn uma_zfree_arg 246allow to 247specify an argument for the 248.Dv ctor 249and 250.Dv dtor 251functions, respectively. 252.Pp 253Created zones, 254which are empty, 255can be destroyed using 256.Fn uma_zdestroy , 257freeing all memory that was allocated for the zone. 258All items allocated from the zone with 259.Fn uma_zalloc 260must have been freed with 261.Fn uma_zfree 262before. 263.Pp 264The 265.Fn uma_zone_set_max 266function limits the number of items 267.Pq and therefore memory 268that can be allocated to 269.Fa zone . 270The 271.Fa nitems 272argument specifies the requested upper limit number of items. 273The effective limit is returned to the caller, as it may end up being higher 274than requested due to the implementation rounding up to ensure all memory pages 275allocated to the zone are utilised to capacity. 276The limit applies to the total number of items in the zone, which includes 277allocated items, free items and free items in the per-cpu caches. 278On systems with more than one CPU it may not be possible to allocate 279the specified number of items even when there is no shortage of memory, 280because all of the remaining free items may be in the caches of the 281other CPUs when the limit is hit. 282.Pp 283The 284.Fn uma_zone_get_max 285function returns the effective upper limit number of items for a zone. 286.Pp 287The 288.Fn uma_zone_get_cur 289function returns the approximate current occupancy of the zone. 290The returned value is approximate because appropriate synchronisation to 291determine an exact value is not performed by the implementation. 292This ensures low overhead at the expense of potentially stale data being used 293in the calculation. 294.Pp 295The 296.Fn uma_zone_set_warning 297function sets a warning that will be printed on the system console when the 298given zone becomes full and fails to allocate an item. 299The warning will be printed no more often than every five minutes. 300Warnings can be turned off globally by setting the 301.Va vm.zone_warnings 302sysctl tunable to 303.Va 0 . 304.Pp 305The 306.Fn uma_zone_set_maxaction 307function sets a function that will be called when the given zone becomes full 308and fails to allocate an item. 309The function will be called with the zone locked. 310Also, the function 311that called the allocation function may have held additional locks. 312Therefore, 313this function should do very little work (similar to a signal handler). 314.Pp 315The 316.Fn SYSCTL_UMA_MAX parent nbr name access zone descr 317macro declares a static 318.Xr sysctl 319oid that exports the effective upper limit number of items for a zone. 320The 321.Fa zone 322argument should be a pointer to 323.Vt uma_zone_t . 324A read of the oid returns value obtained through 325.Fn uma_zone_get_max . 326A write to the oid sets new value via 327.Fn uma_zone_set_max . 328The 329.Fn SYSCTL_ADD_UMA_MAX ctx parent nbr name access zone descr 330macro is provided to create this type of oid dynamically. 331.Pp 332The 333.Fn SYSCTL_UMA_CUR parent nbr name access zone descr 334macro declares a static read-only 335.Xr sysctl 336oid that exports the approximate current occupancy of the zone. 337The 338.Fa zone 339argument should be a pointer to 340.Vt uma_zone_t . 341A read of the oid returns value obtained through 342.Fn uma_zone_get_cur . 343The 344.Fn SYSCTL_ADD_UMA_CUR ctx parent nbr name zone descr 345macro is provided to create this type of oid dynamically. 346.Sh RETURN VALUES 347The 348.Fn uma_zalloc 349function returns a pointer to an item, or 350.Dv NULL 351if the zone ran out of unused items 352and 353.Dv M_NOWAIT 354was specified. 355.Sh SEE ALSO 356.Xr malloc 9 357.Sh HISTORY 358The zone allocator first appeared in 359.Fx 3.0 . 360It was radically changed in 361.Fx 5.0 362to function as a slab allocator. 363.Sh AUTHORS 364.An -nosplit 365The zone allocator was written by 366.An John S. Dyson . 367The zone allocator was rewritten in large parts by 368.An Jeff Roberson Aq Mt jeff@FreeBSD.org 369to function as a slab allocator. 370.Pp 371This manual page was written by 372.An Dag-Erling Sm\(/orgrav Aq Mt des@FreeBSD.org . 373Changes for UMA by 374.An Jeroen Ruigrok van der Werven Aq Mt asmodai@FreeBSD.org . 375