151 lines
4.9 KiB
Groff
151 lines
4.9 KiB
Groff
.\"-
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.\" Copyright (c) 2001 Dag-Erling Coïdan Smørgrav
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 27, 2001
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.Dt ZONE 9
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.Os
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.Sh NAME
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.Nm uma_zcreate ,
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.Nm uma_zalloc ,
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.Nm uma_zfree ,
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.Nm uma_zdestroy
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.Nd zone allocator
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/queue.h
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.In vm/uma.h
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.Ft uma_zone_t
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.Fn uma_zcreate "char *name" "int size" "uma_ctor ctor" "uma_dtor dtor" "uma_in
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it uminit" "uma_fini fini" "int align" "u_int16_t flags"
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.Ft void *
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.Fn uma_zalloc "uma_zone_t zone, int flags"
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.Ft void
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.Fn uma_zfree "uma_zone_t zone" "void *item"
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.Ft void
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.Fn uma_zdestroy "uma_zone_t zone"
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.Sh DESCRIPTION
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The zone allocator provides an efficient interface for managing
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dynamically-sized collections of items of similar size.
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The zone allocator can work with preallocated zones as well as with
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runtime-allocated ones, and is therefore available much earlier in the
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boot process than other memory management routines.
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.Pp
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A zone is an extensible collection of items of identical size.
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The zone allocator keeps track of which items are in use and which
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are not, and provides functions for allocating items from the zone and
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for releasing them back (which makes them available for later use).
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.Pp
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The zone allocator stores state information inside the items proper
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while they are not allocated,
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so structures that will be managed by the zone allocator
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and wish to use the type stable property of zones by leaving some fields
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pre-filled between allocations, must reserve
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two pointers at the very beginning for internal use by the zone
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allocator, as follows:
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.Bd -literal
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struct my_item {
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struct my_item *z_rsvd1;
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struct my_item *z_rsvd2;
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/* rest of structure */
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};
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.Ed
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.Pp
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Alternatively they should assume those entries corrupted
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after each allocation.
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After the first allocation of an item,
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it will have been cleared to zeroes, however subsequent allocations
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will retain the contents as of the last free, with the exception of the
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fields mentioned above.
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.Pp
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The
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.Fn uma_zcreate
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function creates a new zone from which items may then be allocated from.
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The
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.Fa name
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argument is a text name of the zone for debugging and stats; this memory
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should not be freed until the zone has been deallocated.
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.Pp
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To allocate an item from a zone, simply call
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.Fn uma_zalloc
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with a pointer to that zone
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and set the
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.Fa flags
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argument to selected flags as documented in
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.Xr malloc 9 .
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It will return a pointer to an item if successful,
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or
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.Dv NULL
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in the rare case where all items in the zone are in use and the
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allocator is unable to grow the zone
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or when
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.Dv M_NOWAIT
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is specified.
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.Pp
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Items are released back to the zone from which they were allocated by
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calling
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.Fn uma_zfree
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with a pointer to the zone and a pointer to the item.
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.Pp
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Created zones,
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which are empty,
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can be destroyed using
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.Fn uma_zdestroy ,
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freeing all memory that was allocated for the zone.
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All items allocated from the zone with
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.Fn uma_zalloc
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must have been freed with
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.Fn uma_zfree
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before.
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.Sh RETURN VALUES
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.Pp
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The
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.Fn uma_zalloc
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function returns a pointer to an item, or
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.Dv NULL
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if the zone ran out of unused items and the allocator was unable to
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enlarge it.
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.Sh SEE ALSO
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.Xr malloc 9
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.Sh HISTORY
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The zone allocator first appeared in
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.Fx 3.0 .
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It was radically changed in
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.Fx 5.0
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to function as a slab allocator.
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.Sh AUTHORS
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.An -nosplit
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The zone allocator was written by
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.An John S. Dyson .
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The zone allocator was rewritten in large parts by
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.An Jeff Roberson Aq jeff@FreeBSD.org
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to function as a slab allocator.
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.Pp
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This manual page was written by
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.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org .
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Changes for UMA by
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.An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org .
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