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Man Pages


Manual Reference Pages  -  VMEM (9)

NAME

vmem - general purpose resource allocator

CONTENTS

Synopsis
Description
Return Values
Code References
See Also
History
Authors
Bugs

SYNOPSIS


.In 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

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.
qcache_max
  The largest size of allocations which can be served by quantum cache. It is merely a hint and can be ignored.
flags Combination of malloc(9) wait flag and vmem allocation strategy flag:
M_FIRSTFIT
  Prefer allocation performance.
M_BESTFIT Prefer space efficiency.

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 and M_BESTFIT.
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.

RETURN VALUES

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.

CODE REFERENCES

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

SEE ALSO

malloc(9)
.Rs Magazines and Vmem: Extending the Slab Allocator to Many CPUs and Arbitrary Resources
.Re

HISTORY

The vmem allocator was originally implemented in
.Nx . It was introduced in
.Fx 10.0 .

AUTHORS


.An -nosplit Original implementation of vmem was written by
.An YAMAMOTO Takashi . The
.Fx port was made by
.An Jeff Roberson .

BUGS

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