7d39a491bf
This is described in the vmem paper: "directs vmem to use the next free segment after the one previously allocated." The implementation adds a new boundary tag type, M_CURSOR, which is linked into the segment list and precedes the segment following the previous M_NEXTFIT allocation. The cursor is used to locate the next free segment satisfying the allocation constraints. This implementation isn't O(1) since busy tags aren't coalesced, and we may potentially scan the entire segment list during an M_NEXTFIT allocation. Reviewed by: alc MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D17226
313 lines
8.0 KiB
Groff
313 lines
8.0 KiB
Groff
.\" $NetBSD: vmem.9,v 1.15 2013/01/29 22:02:17 wiz Exp $
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.\"
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.\" Copyright (c)2006 YAMAMOTO Takashi,
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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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.\" ------------------------------------------------------------
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.Dd May 17, 2019
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.Dt VMEM 9
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.Os
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.\" ------------------------------------------------------------
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.Sh NAME
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.Nm vmem
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.Nd general purpose resource allocator
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.\" ------------------------------------------------------------
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.Sh SYNOPSIS
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.In sys/vmem.h
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft vmem_t *
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.Fn vmem_create \
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"const char *name" "vmem_addr_t base" "vmem_size_t size" "vmem_size_t quantum" \
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"vmem_size_t qcache_max" "int flags"
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft int
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.Fn vmem_add \
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"vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size" "int flags"
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft int
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.Fn vmem_xalloc \
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"vmem_t *vm" "const vmem_size_t size" "vmem_size_t align" \
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"const vmem_size_t phase" "const vmem_size_t nocross" \
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"const vmem_addr_t minaddr" "const vmem_addr_t maxaddr" "int flags" \
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"vmem_addr_t *addrp"
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft void
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.Fn vmem_xfree "vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size"
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft int
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.Fn vmem_alloc "vmem_t *vm" "vmem_size_t size" "int flags" "vmem_addr_t *addrp"
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft void
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.Fn vmem_free "vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size"
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft void
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.Fn vmem_destroy "vmem_t *vm"
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.\" ------------------------------------------------------------
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.Sh DESCRIPTION
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The
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.Nm
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is a general purpose resource allocator.
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Despite its name, it can be used for arbitrary resources
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other than virtual memory.
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.Pp
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Fn vmem_create
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creates a new vmem arena.
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.Bl -tag -width qcache_max
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.It Fa name
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The string to describe the vmem.
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.It Fa base
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The start address of the initial span.
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Pass
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.Dv 0
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if no initial span is required.
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.It Fa size
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The size of the initial span.
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Pass
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.Dv 0
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if no initial span is required.
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.It Fa quantum
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The smallest unit of allocation.
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.It Fa qcache_max
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The largest size of allocations which can be served by quantum cache.
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It is merely a hint and can be ignored.
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.It Fa flags
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.Xr malloc 9
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wait flag.
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.El
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.Pp
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Fn vmem_add
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adds a span of size
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.Fa size
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starting at
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.Fa addr
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to the arena.
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Returns
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0
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on success,
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.Dv ENOMEM
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on failure.
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.Fa flags
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is
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.Xr malloc 9
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wait flag.
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.Pp
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Fn vmem_xalloc
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allocates a resource from the arena.
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.Bl -tag -width nocross
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.It Fa vm
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The arena which we allocate from.
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.It Fa size
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Specify the size of the allocation.
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.It Fa align
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If zero, don't care about the alignment of the allocation.
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Otherwise, request a resource segment starting at
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offset
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.Fa phase
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from an
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.Fa align
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aligned boundary.
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.It Fa phase
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See the above description of
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.Fa align .
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If
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.Fa align
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is zero,
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.Fa phase
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should be zero.
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Otherwise,
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.Fa phase
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should be smaller than
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.Fa align .
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.It Fa nocross
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Request a resource which doesn't cross
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.Fa nocross
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aligned boundary.
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.It Fa minaddr
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Specify the minimum address which can be allocated, or
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.Dv VMEM_ADDR_MIN
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if the caller does not care.
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.It Fa maxaddr
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Specify the maximum address which can be allocated, or
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.Dv VMEM_ADDR_MAX
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if the caller does not care.
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.It Fa flags
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A bitwise OR of an allocation strategy and a
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.Xr malloc 9
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wait flag.
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The allocation strategy is one of:
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.Bl -tag width indent
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.It Dv M_FIRSTFIT
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Prefer allocation performance.
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.It Dv M_BESTFIT
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Prefer space efficiency.
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.It Dv M_NEXTFIT
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Perform an address-ordered search for free addresses, beginning where
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the previous search ended.
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.El
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.It Fa addrp
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On success, if
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.Fa addrp
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is not
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.Dv NULL ,
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.Fn vmem_xalloc
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overwrites it with the start address of the allocated span.
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.El
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.Pp
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.\" ------------------------------------------------------------
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.Fn vmem_xfree
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frees resource allocated by
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.Fn vmem_xalloc
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to the arena.
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.Bl -tag -width addr
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.It Fa vm
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The arena which we free to.
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.It Fa addr
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The resource being freed.
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It must be the one returned by
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.Fn vmem_xalloc .
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Notably, it must not be the one from
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.Fn vmem_alloc .
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Otherwise, the behaviour is undefined.
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.It Fa size
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The size of the resource being freed.
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It must be the same as the
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.Fa size
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argument used for
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.Fn vmem_xalloc .
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.El
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.Pp
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Fn vmem_alloc
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allocates a resource from the arena.
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.Bl -tag -width flags
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.It Fa vm
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The arena which we allocate from.
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.It Fa size
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Specify the size of the allocation.
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.It Fa flags
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A bitwise OR of an
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.Nm
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allocation strategy flag (see above) and a
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.Xr malloc 9
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sleep flag.
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.It Fa addrp
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On success, if
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.Fa addrp
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is not
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.Dv NULL ,
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.Fn vmem_alloc
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overwrites it with the start address of the allocated span.
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.El
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.Pp
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Fn vmem_free
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frees resource allocated by
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.Fn vmem_alloc
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to the arena.
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.Bl -tag -width addr
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.It Fa vm
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The arena which we free to.
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.It Fa addr
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The resource being freed.
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It must be the one returned by
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.Fn vmem_alloc .
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Notably, it must not be the one from
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.Fn vmem_xalloc .
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Otherwise, the behaviour is undefined.
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.It Fa size
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The size of the resource being freed.
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It must be the same as the
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.Fa size
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argument used for
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.Fn vmem_alloc .
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.El
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.Pp
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.\" ------------------------------------------------------------
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.Fn vmem_destroy
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destroys a vmem arena.
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.Bl -tag -width vm
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.It Fa vm
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The vmem arena being destroyed.
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The caller should ensure that no one will use it anymore.
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.El
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.\" ------------------------------------------------------------
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.Sh RETURN VALUES
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.Fn vmem_create
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returns a pointer to the newly allocated vmem_t.
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Otherwise, it returns
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.Dv NULL .
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.Pp
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On success,
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.Fn vmem_xalloc
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and
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.Fn vmem_alloc
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return 0.
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Otherwise,
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.Dv ENOMEM
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is returned.
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.\" ------------------------------------------------------------
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.Sh CODE REFERENCES
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The
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.Nm
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subsystem is implemented within the file
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.Pa sys/kern/subr_vmem.c .
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.\" ------------------------------------------------------------
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.Sh SEE ALSO
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.Xr malloc 9
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.Rs
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.%A Jeff Bonwick
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.%A Jonathan Adams
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.%T "Magazines and Vmem: Extending the Slab Allocator to Many CPUs and Arbitrary Resources"
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.%J "2001 USENIX Annual Technical Conference"
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.%D 2001
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.Re
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.\" ------------------------------------------------------------
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.Sh HISTORY
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The
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.Nm
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allocator was originally implemented in
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.Nx .
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It was introduced in
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.Fx 10.0 .
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.Sh AUTHORS
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.An -nosplit
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Original implementation of
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.Nm
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was written by
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.An "YAMAMOTO Takashi" .
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The
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.Fx
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port was made by
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.An "Jeff Roberson" .
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.Sh BUGS
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.Nm
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relies on
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.Xr malloc 9 ,
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so it cannot be used as early during system bootstrap.
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