vmem_add9freebsd

Usage

Overview

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.