Copyright (c) 2001 Dag-Erling Co�dan Sm�rgrav
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
$FreeBSD: head/share/man/man9/zone.9 95787 2002-04-30 09:47:50Z asmodai $
.Dd January 27, 2001 .Dt ZONE 9 .Os .Sh NAME .Nm zinit , .Nm zalloc , .Nm zfree , .Nm zdestroy .Nd zone allocator .Sh SYNOPSIS n sys/param.h n sys/queue.h n vm/uma.h .Ft vm_zone_t .Fn zinit "char *name" "int size" "int nentries" "int flags" "int zalloc" .Ft void * .Fn zalloc "vm_zone_t z" .Ft void .Fn zfree "vm_zone_t z" "void *item" .Ft void .Fn zdestroy "vm_zone_t z" .Sh DESCRIPTION The zone allocator provides an efficient interface for managing dynamically-sized collections of items of similar size. The zone allocator can work with preallocated zones as well as with runtime-allocated ones, and is therefore available much earlier in the boot process than other memory management routines.
p A zone is an extensible collection of items of identical size. The zone allocator keeps track of which items are in use and which are not, and provides functions for allocating items from the zone and for releasing them back (which makes them available for later use).
p The zone allocator stores state information inside the items proper while they are not allocated, so structures that will be managed by the zone allocator and wish to use the type stable property of zones by leaving some fields pre-filled between allocations, must reserve two pointers at the very beginning for internal use by the zone allocator, as follows: d -literal struct my_item { struct my_item *z_rsvd1; struct my_item *z_rsvd2; /* rest of structure */ }; .Ed
p Alternatively they should assume those entries corrupted after each allocation. After the first allocation of an item, it will have been cleared to zeroes, however subsequent allocations will retain the contents as of the last free, with the exception of the fields mentioned above.
p If the VM system is fully initialized, a dynamically allocated zone can be created using .Fn zinit . The .Fa name argument should be a pointer to a short, descriptive name for the zone; it is used for statistics and debugging purposes. The .Fa size and .Fa nentries are the size of the items held by the zone and the initial size (in items) of the zone, respectively. The .Fa flags argument should be set to .Dv ZONE_INTERRUPT if there is a chance that items may be allocated from the zone in interrupt context; note that in this case, the zone will never grow larger than .Fa nentries items. In all other cases, .Fa flags should be set to 0. The final argument, .Fa zalloc , indicates the number of VM pages by which the zone should grow every time it fills up.
p To allocate an item from a zone, simply call .Fn zalloc with a pointer to that zone; it will return a pointer to an item, or .Dv NULL in the rare case where all items in the zone are in use and the allocator is unable to grow the zone.
p Items are released back to the zone from which they were allocated by calling .Fn zfree with a pointer to the zone and a pointer to the item.
p Zones created with .Fn zinit can be destroyed using .Fn zdestroy , freeing all memory that was allocated for the zone. All items allocated from the zone with .Fn zalloc must have been freed with .Fn zfree before. .Sh RETURN VALUES
p The .Fn zinit function returns a pointer to a fully initialized .Vt "struct vm_zone" , or .Dv NULL if it was unable to .Fn malloc a .Vt "struct vm_zone" .
p The .Fn zalloc function returns a pointer to an item, or .Dv NULL if the zone ran out of unused items and the allocator was unable to enlarge it. .Sh SEE ALSO .Xr malloc 9 .Sh HISTORY The zone allocator first appeared in .Fx 3.0 . .Sh AUTHORS .An -nosplit The zone allocator was written by .An John S. Dyson .
p This manual page was written by .An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org .