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 automatic 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 success. 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 quantum 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. 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 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 VALUES

vmem_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 ALSO

intro(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).