KM_ALLOC(9)

NAME
km_alloc, km_free - kernel memory allocator

SYNOPSIS
#include <sys/types.h>
#include <uvm/uvm_extern.h>
void *
km_alloc(size_t sz, const struct kmem_va_mode *kv, const struct kmem_pa_mode *kp, const struct kmem_dyn_mode *kd);
void
km_free(void *v, size_t sz, const struct kmem_va_mode *kv, const struct kmem_pa_mode *kp);

DESCRIPTION
The km_alloc() function allocates kernel virtual space optionally backed by physical pages. The km_free() function frees the space that was previously allocated by km_alloc().

The sz argument specifies the size of the allocation and must be a multiple of PAGE_SIZE. The kv and kp arguments specify the type of virtual and physical memory to be allocated. The kd argument specifies additional options for the allocation. The arguments passed to km_free() must match those that were used to obtain the space in km_alloc().

Typically a user will use certain predefined modes for memory allocation. For virtual space the predefined modes are:

kv_any
    Allocates the virtual space anywhere.
kv_intrsafe
    Allocates the virtual space in the interrupt safe map.
kv_page
    Allocates single pages.

For physical pages the predefined modes are:

kp_dirty
    Maps dirty pages into the allocation.
kp_zero
    Maps zeroed pages into the allocation.
kp_dma
    Maps dma-accessible pages into the allocation.
kp_dma_zero
    Maps zeroed dma-accessible pages into the allocation.
kp_pageable
    Pages will be demand paged.
kp_none
    Leaves the allocation unmapped.

The other parameters for allocation are:

kd_waitok
    Sleeping for physical pages is allowed.
kd_nowait
    Sleeping is not allowed.
kd_trylock
    Fail if the allocator cannot obtain locks without waiting.

In case the predefined allocation modes are not sufficient, a custom allocation mode can be created. The structure controlling the virtual space allocation is:

    struct kmem_va_mode {
    	struct vm_map **kv_map;
    	vsize_t kv_align;
    	int kv_wait;
    	int kv_singlepage;
    };

kv_map
    A pointer to the pointer to the uvm_map the space will be allocated from.

kv_align
    Alignment constraint of the allocated space.

kv_wait
    A flag indicating whether the allocator should wait for space to be freed if the allocation cannot be satisfied.

kv_singlepage
    A flag indicating if the allocations will always be for single pages.

    struct kmem_pa_mode {
    	struct uvm_constraint_range *kp_constraint;
    	struct uvm_object **kp_object;
    	paddr_t kp_align;
    	paddr_t kp_boundary;
    	int kp_nomem;
    	int kp_maxseg;
    	int kp_zero;
    	int kp_pageable;
    };

kp_constraint
    A pointer to physical allocation constraints.

kp_object
    A pointer to a pointer to a uvm_object if the pages should be backed by a kernel object.

kp_align
    Physical alignment of the first page in the allocation.

kp_boundary
    Boundary that the physical addresses can't cross if the allocation is contiguous.

kp_nomem
    A flag that specifies that the allocation should not be backed by physical pages.

kp_maxseg
    Maximal amount of contiguous physical segments in the allocation.

kp_zero
    A flag that specifies if the returned memory should be zeroed.

kp_pageable
    A flag that specifies if the returned memory should be demand paged from the backing object instead of being allocated up front.

    struct kmem_dyn_mode {
    	int kd_waitok;
    	int kd_trylock;
    	voff_t kd_prefer;
    	int *kd_slowdown;
    };

kd_waitok
    A flag that specifies if the allocator may sleep waiting for memory.

kd_trylock
    A flag that specifies if the allocator should fail if it can't immediately obtain a lock.

kd_prefer
    An offset given to PMAP_PREFER to virtually align the allocated space.

kd_slowdown
    A pointer to an integer that will be set to 1 if the internal single page allocator needs the caller to back off to allow the allocator to catch up.

RETURN VALUES
km_alloc() returns a kernel virtual address or NULL if the allocation cannot be satisfied.

SEE ALSO
malloc(9), uvm(9)