VMEM(9)

VMEM(9) | 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, 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);

# 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, 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 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:
  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_xcreate() 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).

January 29, 2013 | NetBSD 7.1