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Manual Pages  — VMEM

NAME

vmem – general purpose resource allocator

CONTENTS

SYNOPSIS

#include <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 malloc(9) wait flag.

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
  Prefer allocation performance.
M_BESTFIT Prefer space efficiency.
M_NEXTFIT Perform an address-ordered search for free addresses, beginning where the previous search ended.
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)

Jeff Bonwick, Jonathan Adams, 2001 USENIX Annual Technical Conference, Magazines and Vmem: Extending the Slab Allocator to Many CPUs and Arbitrary Resources, 2001.

HISTORY

The vmem allocator was originally implemented in NetBSD It was introduced in FreeBSD 10.0 .

AUTHORS

Original implementation of vmem was written by YAMAMOTO Takashi. The FreeBSD port was made by Jeff Roberson.

BUGS

vmem relies on malloc(9), so it cannot be used as early during system bootstrap.
VMEM (9) May 17, 2019
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