man/man9/vmem.9

.\"	$NetBSD: vmem.9,v 1.15 2013/01/29 22:02:17 wiz Exp $
.\"
.\" Copyright (c)2006 YAMAMOTO Takashi,
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" ------------------------------------------------------------
.Dd May 17, 2019
.Dt VMEM 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm vmem
.Nd general purpose resource allocator
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/vmem.h
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft vmem_t *
.Fn vmem_create \
"const char *name" "vmem_addr_t base" "vmem_size_t size" "vmem_size_t quantum" \
"vmem_size_t qcache_max" "int flags"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_add \
"vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size" "int flags"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_xalloc \
"vmem_t *vm" "const vmem_size_t size" "vmem_size_t align" \
"const vmem_size_t phase" "const vmem_size_t nocross" \
"const vmem_addr_t minaddr" "const vmem_addr_t maxaddr" "int flags" \
"vmem_addr_t *addrp"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn vmem_xfree "vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_alloc "vmem_t *vm" "vmem_size_t size" "int flags" "vmem_addr_t *addrp"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn vmem_free "vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn vmem_destroy "vmem_t *vm"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
The
.Nm
is a general purpose resource allocator.
Despite its name, it can be used for arbitrary resources
other than virtual memory.
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_create
creates a new vmem arena.
.Bl -tag -width qcache_max
.It Fa name
The string to describe the vmem.
.It Fa base
The start address of the initial span.
Pass
.Dv 0
if no initial span is required.
.It Fa size
The size of the initial span.
Pass
.Dv 0
if no initial span is required.
.It Fa quantum
The smallest unit of allocation.
.It Fa qcache_max
The largest size of allocations which can be served by quantum cache.
It is merely a hint and can be ignored.
.It Fa flags
.Xr malloc 9
wait flag.
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_add
adds a span of size
.Fa size
starting at
.Fa addr
to the arena.
Returns
0
on success,
.Dv ENOMEM
on failure.
.Fa flags
is
.Xr malloc 9
wait flag.
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xalloc
allocates a resource from the arena.
.Bl -tag -width nocross
.It Fa vm
The arena which we allocate from.
.It Fa size
Specify the size of the allocation.
.It Fa align
If zero, don't care about the alignment of the allocation.
Otherwise, request a resource segment starting at
offset
.Fa phase
from an
.Fa align
aligned boundary.
.It Fa phase
See the above description of
.Fa align .
If
.Fa align
is zero,
.Fa phase
should be zero.
Otherwise,
.Fa phase
should be smaller than
.Fa align .
.It Fa nocross
Request a resource which doesn't cross
.Fa nocross
aligned boundary.
.It Fa minaddr
Specify the minimum address which can be allocated, or
.Dv VMEM_ADDR_MIN
if the caller does not care.
.It Fa maxaddr
Specify the maximum address which can be allocated, or
.Dv VMEM_ADDR_MAX
if the caller does not care.
.It Fa flags
A bitwise OR of an allocation strategy and a
.Xr malloc 9
wait flag.
The allocation strategy is one of:
.Bl -tag width indent
.It Dv M_FIRSTFIT
Prefer allocation performance.
.It Dv M_BESTFIT
Prefer space efficiency.
.It Dv M_NEXTFIT
Perform an address-ordered search for free addresses, beginning where
the previous search ended.
.El
.It Fa addrp
On success, if
.Fa addrp
is not
.Dv NULL ,
.Fn vmem_xalloc
overwrites it with the start address of the allocated span.
.El
.Pp
.\" ------------------------------------------------------------
.Fn vmem_xfree
frees resource allocated by
.Fn vmem_xalloc
to the arena.
.Bl -tag -width addr
.It Fa vm
The arena which we free to.
.It Fa addr
The resource being freed.
It must be the one returned by
.Fn vmem_xalloc .
Notably, it must not be the one from
.Fn vmem_alloc .
Otherwise, the behaviour is undefined.
.It Fa size
The size of the resource being freed.
It must be the same as the
.Fa size
argument used for
.Fn vmem_xalloc .
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_alloc
allocates a resource from the arena.
.Bl -tag -width flags
.It Fa vm
The arena which we allocate from.
.It Fa size
Specify the size of the allocation.
.It Fa flags
A bitwise OR of an
.Nm
allocation strategy flag (see above) and a
.Xr malloc 9
sleep flag.
.It Fa addrp
On success, if
.Fa addrp
is not
.Dv NULL ,
.Fn vmem_alloc
overwrites it with the start address of the allocated span.
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_free
frees resource allocated by
.Fn vmem_alloc
to the arena.
.Bl -tag -width addr
.It Fa vm
The arena which we free to.
.It Fa addr
The resource being freed.
It must be the one returned by
.Fn vmem_alloc .
Notably, it must not be the one from
.Fn vmem_xalloc .
Otherwise, the behaviour is undefined.
.It Fa size
The size of the resource being freed.
It must be the same as the
.Fa size
argument used for
.Fn vmem_alloc .
.El
.Pp
.\" ------------------------------------------------------------
.Fn vmem_destroy
destroys a vmem arena.
.Bl -tag -width vm
.It Fa vm
The vmem arena being destroyed.
The caller should ensure that no one will use it anymore.
.El
.\" ------------------------------------------------------------
.Sh RETURN VALUES
.Fn vmem_create
returns a pointer to the newly allocated vmem_t.
Otherwise, it returns
.Dv NULL .
.Pp
On success,
.Fn vmem_xalloc
and
.Fn vmem_alloc
return 0.
Otherwise,
.Dv ENOMEM
is returned.
.\" ------------------------------------------------------------
.Sh CODE REFERENCES
The
.Nm
subsystem is implemented within the file
.Pa sys/kern/subr_vmem.c .
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr malloc 9
.Rs
.%A Jeff Bonwick
.%A Jonathan Adams
.%T "Magazines and Vmem: Extending the Slab Allocator to Many CPUs and Arbitrary Resources"
.%J "2001 USENIX Annual Technical Conference"
.%D 2001
.Re
.\" ------------------------------------------------------------
.Sh HISTORY
The
.Nm
allocator was originally implemented in
.Nx .
It was introduced in
.Fx 10.0 .
.Sh AUTHORS
.An -nosplit
Original implementation of
.Nm
was written by
.An "YAMAMOTO Takashi" .
The
.Fx
port was made by
.An "Jeff Roberson" .
.Sh BUGS
.Nm
relies on
.Xr malloc 9 ,
so it cannot be used as early during system bootstrap.