VMEM(9) BSD Kernel Developer's Manual VMEM(9)NAME
vmem — virtual memory allocator
SYNOPSIS
#include <sys/vmem.h>
vmem_t *
vmem_create(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);
int
vmem_add(vmem_t *vm, vmem_addr_t addr, vmem_size_t size, vm_flag_t flags,
vmem_addr_t *addrp);
int
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);
void
vmem_xfree(vmem_t *vm, vmem_addr_t addr, vmem_size_t size);
int
vmem_alloc(vmem_t *vm, vmem_size_t size, vm_flag_t 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);
DESCRIPTION
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.
allocfn The callback function used to import spans from the backend
arena. Set both allocfn and freefn to NULL to disable auto‐
matic imports. vmem calls (*allocfn)(arg, size, &actualsize,
flags, &addrp) to import a span of size at least size.
allocfn should accept the same flags as vmem_alloc().
allocfn must return ENOMEM to indicate failure, or 0 on suc‐
cess. If allocfn succeeds, it must write the actual size of
the allocation to actualsize and the starting address of the
imported span to addrp. The actual size will always be
greater than or equal to the requested size.
freefn The callback function used to free spans to the backend
arena. freefn may be NULL even if allocfn is not NULL. vmem
calls (*freefn)(arg, addr, size) to return to arg a span of
size size, starting at addr, that was previously allocated by
allocfn.
arg The backend arena. arg may be NULL. vmem passes arg as the
first argument of allocfn and freefn.
qcache_max The largest size of allocations which can be served by quan‐
tum cache. It is merely a hint and can be ignored.
flags Either of:
VM_SLEEP Can sleep until enough resources are available.
VM_NOSLEEP Don't sleep. Immediately return NULL if there
are not enough resources available.
ipl Interrupt level to be blocked for allocating from vmem.
vmem_add() adds a span of size size starting at addr to the arena.
Returns 0 on success, ENOMEM on failure. flags should be one of:
VM_SLEEP Can sleep until enough resources are available.
VM_NOSLEEP Don't sleep. Immediately return ENOMEM if there are not
enough resources available.
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. Oth‐
erwise, 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 sleep flag.
The allocation strategy is one of:
VM_BESTFIT Prefer space efficiency.
VM_INSTANTFIT Prefer performance.
The sleep flag should be one of:
VM_SLEEP Can sleep until enough resources are available.
VM_NOSLEEP Don't sleep. Immediately return ENOMEM if there are
not enough resources available.
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 allocation strategy and a sleep flag.
The allocation strategy is one of:
VM_BESTFIT Prefer space efficiency.
VM_INSTANTFIT Prefer performance.
The sleep flag should be one of:
VM_SLEEP Can sleep until enough resources are available.
VM_NOSLEEP Don't sleep. Immediately return ENOMEM if there are
not enough resources available.
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.
RETURN VALUESvmem_create() return 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.
CODE REFERENCES
The vmem subsystem is implemented within the file sys/kern/subr_vmem.c.
SEE ALSOintro(9), kmem(9), memoryallocators(9), uvm(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.
AUTHORS
This implementation of vmem was written by YAMAMOTO Takashi.
BUGS
vmem relies on malloc(9), pool(9), and RUN_ONCE(9), so it cannot be used
as early during system bootstrap as extent(9).
BSD September 2, 2011 BSD
