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VMEM(9) Kernel Developer's Manual VMEM(9)

vmem — virtual memory allocator

#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, 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);

vmem_t *
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);

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);

The vmem is a general purpose resource allocator. Despite its name, it can be used for arbitrary resources other than virtual memory.

() 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, flags, &addrp); to import a span of size at least size. allocfn must accept the same flags as (). allocfn must return ENOMEM to indicate failure, or 0 on success. If allocfn succeeds, it must write the starting address of the imported span to addrp.
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:
If the allocation cannot be satisfied immediately, sleep until enough resources are available.
Don't sleep. Immediately return NULL if there are not enough resources available.
ipl
Interrupt level to be blocked for allocating from vmem.

() 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 must accept the same flags as (). 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:
If the allocation cannot be satisfied immediately, sleep until enough resources are available.
Don't sleep. Immediately return NULL if there are not enough resources available.
ipl
Interrupt level to be blocked for allocating from vmem.

() adds a span of size size starting at addr to the arena. Returns 0 on success, ENOMEM on failure.

flags
Either of:
If the allocation cannot be satisfied immediately, sleep until enough resources are available.
Don't sleep. Immediately return ENOMEM if there are not enough resources available.

() 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 must be zero. Otherwise, phase must 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 must be one of:

Prefer space efficiency.
Prefer performance.

The sleep flag must be one of:

If the allocation cannot be satisfied immediately, sleep until enough resources are available.
Don't sleep. Immediately return ENOMEM if there are not enough resources available.
addrp
On success, if addrp is not NULL, () overwrites it with the start address of the allocated span.

() frees resource allocated by vmem_xalloc() to the arena.

vm
The arena which we free to.
addr
The resource being freed. It must have been allocated via (). Notably, it must not have been allocated via 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().

() 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 must be one of:

Prefer space efficiency.
Prefer performance.

The sleep flag must be one of:

If the allocation cannot be satisfied immediately, sleep until enough resources are available.
Don't sleep. Immediately return ENOMEM if there are not enough resources available.
addrp
On success, if addrp is not NULL, () overwrites it with the start address of the allocated span.

() frees resource allocated by vmem_alloc() to the arena.

vm
The arena which we free to.
addr
The resource being freed. It must have been allocated via (). Notably, it must not have been allocated via 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().

() destroys a vmem arena.

vm
The vmem arena being destroyed. The caller must ensure that no one will use it anymore.

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.

The vmem subsystem is implemented within the file sys/kern/subr_vmem.c.

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.

This implementation of vmem was written by YAMAMOTO Takashi.

vmem relies on malloc(9), pool(9), and RUN_ONCE(9), so it cannot be used as early during system bootstrap as extent(9).

February 28, 2016 NetBSD-9.2