vmem
—
general purpose resource allocator
#include <sys/vmem.h>
vmem_t *
vmem_create
(const
char *name, vmem_addr_t
base, vmem_size_t
size, vmem_size_t
quantum, vmem_size_t
qcache_max, int
flags);
int
vmem_add
(vmem_t
*vm, vmem_addr_t
addr, vmem_size_t
size, int
flags);
int
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);
void
vmem_xfree
(vmem_t
*vm, vmem_addr_t
addr, vmem_size_t
size);
int
vmem_alloc
(vmem_t
*vm, vmem_size_t
size, int flags,
vmem_addr_t *addrp);
void
vmem_free
(vmem_t
*vm, vmem_addr_t
addr, vmem_size_t
size);
void
vmem_destroy
(vmem_t
*vm);
The vmem
is a general purpose resource allocator.
Despite its name, it can be used for arbitrary resources other than virtual
memory.
vmem_create
() creates a new vmem
arena.
- name
- The string to describe the vmem.
- base
- The start address of the initial span. Pass
0
if
no initial span is required.
- size
- The size of the initial span. Pass
0
if no initial
span is required.
- quantum
- The smallest unit of allocation.
- qcache_max
- The largest size of allocations which can be served by quantum cache. It
is merely a hint and can be ignored.
- flags
- malloc(9)
wait flag.
vmem_add
() adds a span of size
size starting at addr to the
arena. Returns 0 on success, ENOMEM
on failure.
flags is
malloc(9)
wait flag.
vmem_xalloc
() allocates a resource from
the arena.
- vm
- The arena which we allocate from.
- size
- Specify the size of the allocation.
- align
- If zero, don't care about the alignment of the allocation. Otherwise,
request a resource segment starting at offset phase
from an align aligned boundary.
- phase
- See the above description of align. If
align is zero, phase should be
zero. Otherwise, phase should be smaller than
align.
- nocross
- Request a resource which doesn't cross nocross
aligned boundary.
- minaddr
- Specify the minimum address which can be allocated, or
VMEM_ADDR_MIN
if the caller does not care.
- maxaddr
- Specify the maximum address which can be allocated, or
VMEM_ADDR_MAX
if the caller does not care.
- flags
- A bitwise OR of an allocation strategy and a
malloc(9)
wait flag. The allocation strategy is one of:
M_FIRSTFIT
- Prefer allocation performance.
M_BESTFIT
- Prefer space efficiency.
M_NEXTFIT
- Perform an address-ordered search for free addresses, beginning where
the previous search ended.
- addrp
- On success, if addrp is not
NULL
, vmem_xalloc
()
overwrites it with the start address of the allocated span.
vmem_xfree
() frees resource allocated by
vmem_xalloc
() to the arena.
- vm
- The arena which we free to.
- addr
- The resource being freed. It must be the one returned by
vmem_xalloc
(). Notably, it must not be the one
from vmem_alloc
(). Otherwise, the behaviour is
undefined.
- size
- The size of the resource being freed. It must be the same as the
size argument used for
vmem_xalloc
().
vmem_alloc
() allocates a resource from the
arena.
- vm
- The arena which we allocate from.
- size
- Specify the size of the allocation.
- flags
- A bitwise OR of an
vmem
allocation strategy flag
(see above) and a
malloc(9)
sleep flag.
- addrp
- On success, if addrp is not
NULL
, vmem_alloc
()
overwrites it with the start address of the allocated span.
vmem_free
() frees resource allocated by
vmem_alloc
() to the arena.
- vm
- The arena which we free to.
- addr
- The resource being freed. It must be the one returned by
vmem_alloc
(). Notably, it must not be the one from
vmem_xalloc
(). Otherwise, the behaviour is
undefined.
- size
- The size of the resource being freed. It must be the same as the
size argument used for
vmem_alloc
().
vmem_destroy
() destroys a vmem arena.
- vm
- The vmem arena being destroyed. The caller should ensure that no one will
use it anymore.
vmem_create
() returns a pointer to the newly allocated
vmem_t. Otherwise, it returns NULL
.
On success, vmem_xalloc
() and
vmem_alloc
() return 0. Otherwise,
ENOMEM
is returned.
The vmem
subsystem is implemented within the file
sys/kern/subr_vmem.c.
malloc(9)
Jeff Bonwick and
Jonathan Adams, Magazines and
Vmem: Extending the Slab Allocator to Many CPUs and Arbitrary
Resources, 2001 USENIX Annual Technical
Conference, 2001.
The vmem
allocator was originally implemented in
NetBSD. It was introduced in FreeBSD
10.0.
Original implementation of vmem
was written by
YAMAMOTO Takashi. The FreeBSD
port was made by Jeff Roberson.
vmem
relies on
malloc(9),
so it cannot be used as early during system bootstrap.