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 February 7, 2014 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_find_refcnt , 38.Nm uma_zdestroy , 39.Nm uma_zone_set_max, 40.Nm uma_zone_get_max, 41.Nm uma_zone_get_cur, 42.Nm uma_zone_set_warning 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 "uint32_t *" 63.Fn uma_find_refcnt "uma_zone_t zone" "void *item" 64.Ft void 65.Fn uma_zdestroy "uma_zone_t zone" 66.Ft int 67.Fn uma_zone_set_max "uma_zone_t zone" "int nitems" 68.Ft int 69.Fn uma_zone_get_max "uma_zone_t zone" 70.Ft int 71.Fn uma_zone_get_cur "uma_zone_t zone" 72.Ft void 73.Fn uma_zone_set_warning "uma_zone_t zone" "const char *warning" 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_REFCNT 156Each item in the zone would have internal reference counter associated with it. 157See 158.Fn uma_find_refcnt . 159.It Dv UMA_ZONE_NODUMP 160Pages belonging to the zone will not be included into mini-dumps. 161.It Dv UMA_ZONE_PCPU 162An allocation from zone would have 163.Va mp_ncpu 164shadow copies, that are privately assigned to CPUs. 165A CPU can address its private copy using base allocation address plus 166multiple of current CPU id and 167.Fn sizeof "struct pcpu" : 168.Bd -literal -offset indent 169foo_zone = uma_zcreate(..., UMA_ZONE_PCPU); 170 ... 171foo_base = uma_zalloc(foo_zone, ...); 172 ... 173critical_enter(); 174foo_pcpu = (foo_t *)zpcpu_get(foo_base); 175/* do something with foo_pcpu */ 176critical_exit(); 177.Ed 178.It Dv UMA_ZONE_OFFPAGE 179By default book-keeping of items within a slab is done in the slab page itself. 180This flag explicitly tells subsystem that book-keeping structure should be 181allocated separately from special internal zone. 182This flag requires either 183.Dv UMA_ZONE_VTOSLAB 184or 185.Dv UMA_ZONE_HASH , 186since subsystem requires a mechanism to find a book-keeping structure 187to an item beeing freed. 188The subsystem may choose to prefer offpage book-keeping for certain zones 189implicitly. 190.It Dv UMA_ZONE_ZINIT 191The zone will have its 192.Ft uma_init 193method set to internal method that initializes a new allocated slab 194to all zeros. 195Do not mistake 196.Ft uma_init 197method with 198.Ft uma_ctor . 199A zone with 200.Dv UMA_ZONE_ZINIT 201flag would not return zeroed memory on every 202.Fn uma_zalloc . 203.It Dv UMA_ZONE_HASH 204The zone should use an internal hash table to find slab book-keeping 205structure where an allocation being freed belongs to. 206.It Dv UMA_ZONE_VTOSLAB 207The zone should use special field of 208.Vt vm_page_t 209to find slab book-keeping structure where an allocation being freed belongs to. 210.It Dv UMA_ZONE_MALLOC 211The zone is for the 212.Xr malloc 9 213subsystem. 214.It Dv UMA_ZONE_VM 215The zone is for the VM subsystem. 216.El 217.Pp 218To allocate an item from a zone, simply call 219.Fn uma_zalloc 220with a pointer to that zone 221and set the 222.Fa flags 223argument to selected flags as documented in 224.Xr malloc 9 . 225It will return a pointer to an item if successful, 226or 227.Dv NULL 228in the rare case where all items in the zone are in use and the 229allocator is unable to grow the zone 230and 231.Dv M_NOWAIT 232is specified. 233.Pp 234Items are released back to the zone from which they were allocated by 235calling 236.Fn uma_zfree 237with a pointer to the zone and a pointer to the item. 238If 239.Fa item 240is 241.Dv NULL , 242then 243.Fn uma_zfree 244does nothing. 245.Pp 246The variations 247.Fn uma_zalloc_arg 248and 249.Fn uma_zfree_arg 250allow to 251specify an argument for the 252.Dv ctor 253and 254.Dv dtor 255functions, respectively. 256.Pp 257If zone was created with 258.Dv UMA_ZONE_REFCNT 259flag, then pointer to reference counter for an item can be retrieved with 260help of the 261.Fn uma_find_refcnt 262function. 263.Pp 264Created zones, 265which are empty, 266can be destroyed using 267.Fn uma_zdestroy , 268freeing all memory that was allocated for the zone. 269All items allocated from the zone with 270.Fn uma_zalloc 271must have been freed with 272.Fn uma_zfree 273before. 274.Pp 275The 276.Fn uma_zone_set_max 277function limits the number of items 278.Pq and therefore memory 279that can be allocated to 280.Fa zone . 281The 282.Fa nitems 283argument specifies the requested upper limit number of items. 284The effective limit is returned to the caller, as it may end up being higher 285than requested due to the implementation rounding up to ensure all memory pages 286allocated to the zone are utilised to capacity. 287The limit applies to the total number of items in the zone, which includes 288allocated items, free items and free items in the per-cpu caches. 289On systems with more than one CPU it may not be possible to allocate 290the specified number of items even when there is no shortage of memory, 291because all of the remaining free items may be in the caches of the 292other CPUs when the limit is hit. 293.Pp 294The 295.Fn uma_zone_get_max 296function returns the effective upper limit number of items for a zone. 297.Pp 298The 299.Fn uma_zone_get_cur 300function returns the approximate current occupancy of the zone. 301The returned value is approximate because appropriate synchronisation to 302determine an exact value is not performed by the implementation. 303This ensures low overhead at the expense of potentially stale data being used 304in the calculation. 305.Pp 306The 307.Fn uma_zone_set_warning 308function sets a warning that will be printed on the system console when the 309given zone becomes full and fails to allocate an item. 310The warning will be printed not often than every five minutes. 311Warnings can be turned off globally by setting the 312.Va vm.zone_warnings 313sysctl tunable to 314.Va 0 . 315.Pp 316The 317.Fn SYSCTL_UMA_MAX parent nbr name access zone descr 318macro declares a static 319.Xr sysctl 320oid that exports the effective upper limit number of items for a zone. 321The 322.Fa zone 323argument should be a pointer to 324.Vt uma_zone_t . 325A read of the oid returns value obtained through 326.Fn uma_zone_get_max . 327A write to the oid sets new value via 328.Fn uma_zone_set_max . 329The 330.Fn SYSCTL_ADD_UMA_MAX ctx parent nbr name access zone descr 331macro is provided to create this type of oid dynamically. 332.Pp 333The 334.Fn SYSCTL_UMA_CUR parent nbr name access zone descr 335macro declares a static read only 336.Xr sysctl 337oid that exports the approximate current occupancy of the zone. 338The 339.Fa zone 340argument should be a pointer to 341.Vt uma_zone_t . 342A read of the oid returns value obtained through 343.Fn uma_zone_get_cur . 344The 345.Fn SYSCTL_ADD_UMA_CUR ctx parent nbr name zone descr 346macro is provided to create this type of oid dynamically. 347.Sh RETURN VALUES 348The 349.Fn uma_zalloc 350function returns a pointer to an item, or 351.Dv NULL 352if the zone ran out of unused items 353and 354.Dv M_NOWAIT 355was specified. 356.Sh SEE ALSO 357.Xr malloc 9 358.Sh HISTORY 359The zone allocator first appeared in 360.Fx 3.0 . 361It was radically changed in 362.Fx 5.0 363to function as a slab allocator. 364.Sh AUTHORS 365.An -nosplit 366The zone allocator was written by 367.An John S. Dyson . 368The zone allocator was rewritten in large parts by 369.An Jeff Roberson Aq Mt jeff@FreeBSD.org 370to function as a slab allocator. 371.Pp 372This manual page was written by 373.An Dag-Erling Sm\(/orgrav Aq Mt des@FreeBSD.org . 374Changes for UMA by 375.An Jeroen Ruigrok van der Werven Aq Mt asmodai@FreeBSD.org . 376