Copyright (c)2006 YAMAMOTO Takashi,
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.
------------------------------------------------------------
.Dd December 2, 2023 .Dt VMEM 9 .Os ------------------------------------------------------------
.Sh NAME .Nm vmem .Nd virtual memory allocator ------------------------------------------------------------
.Sh SYNOPSIS n 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.
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_create
creates a new vmem arena.
l -tag -offset indent -width qcache_max t Fa name The string to describe the vmem.
t Fa base The start address of the initial span.
Pass
.Dv 0
if no initial span is required.
t Fa size The size of the initial span.
Pass
.Dv 0
if no initial span is required.
t Fa quantum The smallest unit of allocation.
t 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 .
t 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 .
t 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 .
t Fa qcache_max The largest size of allocations which can be served by quantum cache.
It is merely a hint and can be ignored.
t Fa flags Either of:
l -tag -width VM_NOSLEEP t Dv VM_SLEEP If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
t Dv VM_NOSLEEP Don't sleep.
Immediately return
.Dv NULL
if there are not enough resources available.
.El
t Fa ipl Interrupt level to be blocked for allocating from vmem.
.El
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xcreate
creates a new vmem arena.
l -tag -offset indent -width qcache_max t Fa name The string to describe the vmem.
t Fa base The start address of the initial span.
Pass
.Dv 0
if no initial span is required.
t Fa size The size of the initial span.
Pass
.Dv 0
if no initial span is required.
t Fa quantum The smallest unit of allocation.
t 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.
t 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 .
t 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 .
t Fa qcache_max The largest size of allocations which can be served by quantum cache.
It is merely a hint and can be ignored.
t Fa flags Either of:
l -tag -width VM_NOSLEEP t Dv VM_SLEEP If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
t Dv VM_NOSLEEP Don't sleep.
Immediately return
.Dv NULL
if there are not enough resources available.
.El
t Fa ipl Interrupt level to be blocked for allocating from vmem.
.El
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.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.
l -tag -offset indent -width flags t Fa flags Either of:
l -tag -width VM_NOSLEEP t Dv VM_SLEEP If the allocation cannot be satisfied immediately, sleep until enough
resources are available.
t Dv VM_NOSLEEP Don't sleep.
Immediately return
.Dv ENOMEM
if there are not enough resources available.
.El
.El
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xalloc
allocates a resource from the arena.
l -tag -offset indent -width nocross t Fa vm The arena which we allocate from.
t Fa size Specify the size of the allocation.
t 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.
t 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 .
t Fa nocross Request a resource which doesn't cross
.Fa nocross
aligned boundary.
t Fa minaddr Specify the minimum address which can be allocated, or
.Dv VMEM_ADDR_MIN
if the caller does not care.
t Fa maxaddr Specify the maximum address which can be allocated, or
.Dv VMEM_ADDR_MAX
if the caller does not care.
t Fa flags A bitwise OR of an allocation strategy and a sleep flag.
p The allocation strategy must be one of: l -tag -width VM_INSTANTFIT t Dv VM_BESTFIT Prefer space efficiency. t Dv VM_INSTANTFIT Prefer performance. .El
p The sleep flag must be one of: l -tag -width VM_NOSLEEP t Dv VM_SLEEP If the allocation cannot be satisfied immediately, sleep until enough resources are available. t Dv VM_NOSLEEP Don't sleep. Immediately return .Dv ENOMEM if there are not enough resources available. .El t 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
p
------------------------------------------------------------
.Fn vmem_xalloc_addr
allocates a specific address from the arena.
The requested address must be aligned with the arena's quantum.
l -tag -offset indent -width flags t Fa vm The arena which we allocate from.
t Fa addr The address to allocate.
t Fa size Specify the size of the allocation.
t Fa flags A sleep flag.
Because a specific address is being allocated, any specified allocation
strategy is ignored.
p The sleep flag must be one of: l -tag -width VM_NOSLEEP t Dv VM_SLEEP If the allocation cannot be satisfied immediately, sleep until the requested range can be allocated. t Dv VM_NOSLEEP Don't sleep. Immediately return .Dv ENOMEM if the requested range is not available. .El .El
p
------------------------------------------------------------
.Fn vmem_xfree
frees resource allocated by
.Fn vmem_xalloc
or
.Fn vmem_xalloc_addr
to the arena.
l -tag -offset indent -width addr t Fa vm The arena which we free to.
t 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.
t 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
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_xfreeall
frees all resources that have been allocated by
.Fn vmem_xalloc
to the arena.
l -tag -offset indent -width addr t 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
o i.e. were created with a non-zero .Fa qcache_max
c . .El
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_alloc
allocates a resource from the arena.
l -tag -offset indent -width flags t Fa vm The arena which we allocate from.
t Fa size Specify the size of the allocation.
t Fa flags A bitwise OR of an allocation strategy and a sleep flag.
p The allocation strategy must be one of: l -tag -width VM_INSTANTFIT t Dv VM_BESTFIT Prefer space efficiency. t Dv VM_INSTANTFIT Prefer performance. .El
p The sleep flag must be one of: l -tag -width VM_NOSLEEP t Dv VM_SLEEP If the allocation cannot be satisfied immediately, sleep until enough resources are available. t Dv VM_NOSLEEP Don't sleep. Immediately return .Dv ENOMEM if there are not enough resources available. .El t 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
p
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn vmem_free
frees resource allocated by
.Fn vmem_alloc
to the arena.
l -tag -offset indent -width addr t Fa vm The arena which we free to.
t 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.
t 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
p
------------------------------------------------------------
.Fn vmem_destroy
destroys a vmem arena.
l -tag -offset indent -width vm t 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.
p .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.
p
.Fn vmem_alloc
and
.Fn vmem_xalloc
return 0 on success, or
.Er ENOMEM
if either:
l -dash t .Dv VM_NOSLEEP
was specified and a matching region could not be allocated immediately;
or
t 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
a 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 .
p .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 .
Indexes created Thu Sep 25 16:09:42 GMT 2025