man/man9/vmem.9

.\"	$NetBSD: vmem.9,v 1.22 2023/12/02 21:02:12 thorpej Exp $
.\"
.\" Copyright (c)2006 YAMAMOTO Takashi,
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    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
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" SUCH DAMAGE.
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.\" ------------------------------------------------------------
.Dd December 2, 2023
.Dt VMEM 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm vmem
.Nd virtual memory 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" \
"int (*allocfn)(void *, vmem_size_t, vm_flag_t, vmem_addr_t *)" \
"void (*freefn)(void *, vmem_addr_t, vmem_size_t)" \
"void *arg" "vmem_size_t qcache_max" "vm_flag_t flags" "int ipl"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft vmem_t *
.Fn vmem_xcreate \
"const char *name" "vmem_addr_t base" "vmem_size_t size" "vmem_size_t quantum" \
"int (*allocfn)(void *, vmem_size_t, vmem_size_t *, vm_flag_t, vmem_addr_t *)" \
"void (*freefn)(void *, vmem_addr_t, vmem_size_t)" \
"void *arg" "vmem_size_t qcache_max" "vm_flag_t flags" "int ipl"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_add \
"vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size" "vm_flag_t flags"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_xalloc \
"vmem_t *vm" "vmem_size_t size" "vmem_size_t align" \
"vmem_size_t phase" "vmem_size_t nocross" "vmem_addr_t minaddr" \
"vmem_addr_t maxaddr" "vm_flag_t flags" "vmem_addr_t *addrp"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_xalloc_addr \
"vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size" "vm_flag_t flags"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn vmem_xfree "vmem_t *vm" "vmem_addr_t addr" "vmem_size_t size"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn vmem_xfreeall "vmem_t *vm"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn vmem_alloc "vmem_t *vm" "vmem_size_t size" "vm_flag_t 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 -offset indent -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 allocfn
The callback function used to import spans from the backend arena.
Set both
.Fa allocfn
and
.Fa freefn
to
.Dv NULL
to disable automatic imports.
.Nm
calls
.Fo "(*allocfn)"
.Fa arg
.Fa size
.Fa flags
.Fa "&addrp"
.Fc
to import a span of size at least
.Fa size .
.Fa allocfn
must accept the same
.Fa flags
as
.Fn vmem_alloc .
.Fa allocfn
must return
.Dv ENOMEM
to indicate failure, or 0 on success.
If
.Fa allocfn
succeeds, it must write the starting address of the imported span to
.Fa addrp .
.It Fa freefn
The callback function used to free spans to the backend arena.
.Fa freefn
may be
.Dv NULL
even if
.Fa allocfn
is not
.Dv NULL .
.Nm
calls
.Fn "(*freefn)" arg addr size
to return to
.Fa arg
a span of size
.Fa size ,
starting at
.Fa addr ,
that was previously allocated by
.Fa allocfn .
.It Fa arg
The backend arena.
.Fa arg
may be
.Dv NULL .
.Nm
passes
.Fa arg
as the first argument of
.Fa allocfn
and
.Fa freefn .
.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
Either of:
.Bl -tag -width VM_NOSLEEP
.It Dv VM_SLEEP
If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
.It Dv VM_NOSLEEP
Don't sleep.
Immediately return
.Dv NULL
if there are not enough resources available.
.El
.It Fa ipl
Interrupt level to be blocked for allocating from vmem.
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xcreate
creates a new vmem arena.
.Bl -tag -offset indent -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 allocfn
The callback function used to import spans from the backend arena.
Set both
.Fa allocfn
and
.Fa freefn
to
.Dv NULL
to disable automatic imports.
.Nm
calls
.Fo "(*allocfn)"
.Fa arg
.Fa size
.Fa "&actualsize"
.Fa flags
.Fa "&addrp"
.Fc
to import a span of size at least
.Fa size .
.Fa allocfn
must accept the same
.Fa flags
as
.Fn vmem_alloc .
.Fa allocfn
must return
.Dv ENOMEM
to indicate failure, or 0 on success.
If
.Fa allocfn
succeeds, it must write the actual size of the allocation to
.Fa actualsize
and the starting address of the imported span to
.Fa addrp .
The actual size will always be greater than or equal to the requested size.
.It Fa freefn
The callback function used to free spans to the backend arena.
.Fa freefn
may be
.Dv NULL
even if
.Fa allocfn
is not
.Dv NULL .
.Nm
calls
.Fn "(*freefn)" arg addr size
to return to
.Fa arg
a span of size
.Fa size ,
starting at
.Fa addr ,
that was previously allocated by
.Fa allocfn .
.It Fa arg
The backend arena.
.Fa arg
may be
.Dv NULL .
.Nm
passes
.Fa arg
as the first argument of
.Fa allocfn
and
.Fa freefn .
.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
Either of:
.Bl -tag -width VM_NOSLEEP
.It Dv VM_SLEEP
If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
.It Dv VM_NOSLEEP
Don't sleep.
Immediately return
.Dv NULL
if there are not enough resources available.
.El
.It Fa ipl
Interrupt level to be blocked for allocating from vmem.
.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.
.Bl -tag -offset indent -width flags
.It Fa flags
Either of:
.Bl -tag -width VM_NOSLEEP
.It Dv VM_SLEEP
If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
.It Dv VM_NOSLEEP
Don't sleep.
Immediately return
.Dv ENOMEM
if there are not enough resources available.
.El
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xalloc
allocates a resource from the arena.
.Bl -tag -offset indent -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
must be zero.
Otherwise,
.Fa phase
must 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 sleep flag.
.Pp
The allocation strategy must be one of:
.Bl -tag -width VM_INSTANTFIT
.It Dv VM_BESTFIT
Prefer space efficiency.
.It Dv VM_INSTANTFIT
Prefer performance.
.El
.Pp
The sleep flag must be one of:
.Bl -tag -width VM_NOSLEEP
.It Dv VM_SLEEP
If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
.It Dv VM_NOSLEEP
Don't sleep.
Immediately return
.Dv ENOMEM
if there are not enough resources available.
.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_xalloc_addr
allocates a specific address from the arena.
The requested address must be aligned with the arena's quantum.
.Bl -tag -offset indent -width flags
.It Fa vm
The arena which we allocate from.
.It Fa addr
The address to allocate.
.It Fa size
Specify the size of the allocation.
.It Fa flags
A sleep flag.
Because a specific address is being allocated, any specified allocation
strategy is ignored.
.Pp
The sleep flag must be one of:
.Bl -tag -width VM_NOSLEEP
.It Dv VM_SLEEP
If the allocation cannot be satisfied immediately, sleep until the
requested range can be allocated.
.It Dv VM_NOSLEEP
Don't sleep.
Immediately return
.Dv ENOMEM
if the requested range is not available.
.El
.El
.Pp
.\" ------------------------------------------------------------
.Fn vmem_xfree
frees resource allocated by
.Fn vmem_xalloc
or
.Fn vmem_xalloc_addr
to the arena.
.Bl -tag -offset indent -width addr
.It Fa vm
The arena which we free to.
.It Fa addr
The resource being freed.
It must have been allocated via
.Fn vmem_xalloc
or
.Fn vmem_xalloc_addr .
Notably, it must not have been allocated via
.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
or
.Fn vmem_xalloc_addr .
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xfreeall
frees all resources that have been allocated by
.Fn vmem_xalloc
to the arena.
.Bl -tag -offset indent -width addr
.It Fa vm
The arena which we free to.
Note that this function is may not be used on arenas
where resources have been allocated using
.Fn vmem_alloc
or arenas that have a quantum cache
.Po
i.e. were created with a non-zero
.Fa qcache_max
.Pc .
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_alloc
allocates a resource from the arena.
.Bl -tag -offset indent -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 allocation strategy and a sleep flag.
.Pp
The allocation strategy must be one of:
.Bl -tag -width VM_INSTANTFIT
.It Dv VM_BESTFIT
Prefer space efficiency.
.It Dv VM_INSTANTFIT
Prefer performance.
.El
.Pp
The sleep flag must be one of:
.Bl -tag -width VM_NOSLEEP
.It Dv VM_SLEEP
If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
.It Dv VM_NOSLEEP
Don't sleep.
Immediately return
.Dv ENOMEM
if there are not enough resources available.
.El
.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 -offset indent -width addr
.It Fa vm
The arena which we free to.
.It Fa addr
The resource being freed.
It must have been allocated via
.Fn vmem_alloc .
Notably, it must not have been allocated via
.Fn vmem_xalloc
or
.Fn vmem_xalloc addr ,
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 -offset indent -width vm
.It Fa vm
The vmem arena being destroyed.
The caller must ensure that no one will use it anymore.
.El
.\" ------------------------------------------------------------
.Sh RETURN VALUES
.Fn vmem_create
and
.Fn vmem_xcreate
return a pointer to the newly allocated vmem_t on success, or
.Dv NULL
if
.Dv VM_NOSLEEP
was specified and memory could not be allocated immediately.
.Pp
.Fn vmem_add
returns 0 on success, or
.Er ENOMEM
if
.Dv VM_NOSLEEP
was specified and memory could not be allocated immediately to record
the region.
.Pp
.Fn vmem_alloc
and
.Fn vmem_xalloc
return 0 on success, or
.Er ENOMEM
if either:
.Bl -dash
.It
.Dv VM_NOSLEEP
was specified and a matching region could not be allocated immediately;
or
.It
non-default
.Fa align ,
.Fa phase ,
or
.Fa nocross
parameters were specified, and a matching region could not be allocated
without calling the backing
.Fa allocfn
passed to
.Fn vmem_create .
.El
.\" ------------------------------------------------------------
.Sh CODE REFERENCES
The
.Nm
subsystem is implemented within the file
.Pa sys/kern/subr_vmem.c .
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr intro 9 ,
.Xr kmem 9 ,
.Xr memoryallocators 9 ,
.Xr uvm 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 AUTHORS
This implementation of
.Nm
was written by
.An YAMAMOTO Takashi .
.Sh BUGS
.Nm
relies on
.Xr malloc 9 ,
.Xr pool 9 ,
and
.Xr RUN_ONCE 9 ,
so it cannot be used as early during system bootstrap as
.Xr extent 9 .
.Pp
.Nm
has no way to pass
.Fa align ,
.Fa phase ,
.Fa nocross ,
.Fa minaddr ,
or
.Fa maxaddr
constraints into the backing allocator
.Fa allocfn ,
so even if
.Dv VM_SLEEP
is specified,
.Fn vmem_alloc
and
.Fn vmem_xalloc
may spuriously fail immediately with
.Fa align ,
.Fa phase ,
or
.Fa nocross ,
or sleep forever with
.Fa minaddr
or
.Fa maxaddr .