contigmalloc,

#include <sys/types.h>
#include <sys/malloc.h>

void *
contigmalloc(unsigned long size, struct malloc_type *type, int flags, vm_paddr_t low, vm_paddr_t high, unsigned long alignment, vm_paddr_t boundary);

void
contigfree(void *addr, unsigned long size, struct malloc_type *type);

The contigmalloc() function allocates size bytes of contiguous physical memory that is aligned to alignment bytes, and which does not cross a boundary of boundary bytes. If successful, the allocation will reside between physical addresses low and high. The returned pointer points to a wired kernel virtual address range of size bytes allocated from the kernel virtual address (KVA) map.

The flags parameter modifies contigmalloc()'s behaviour as follows:

M_ZERO

Causes the allocated physical memory to be zero filled.

M_NOWAIT

Causes contigmalloc() to return NULL if the request cannot be immediately fulfilled due to resource shortage.

Other flags (if present) are ignored.

The contigfree() function deallocates memory allocated by a previous call to contigmalloc().

The contigmalloc() function does not sleep waiting for memory resources to be freed up, but instead actively reclaims pages before giving up. However, unless M_NOWAIT is specified, it may select a page for reclamation that must first be written to backing storage, causing it to sleep.

The contigmalloc() function returns a kernel virtual address if allocation succeeds, or NULL otherwise.

void *p;
p = contigmalloc(8192, M_DEVBUF, M_ZERO, 0, (1L << 22),
    32 * 1024, 1024 * 1024);

Ask for 8192 bytes of zero-filled memory residing between physical address 0 and 4194303 inclusive, aligned to a 32K boundary and not crossing a 1M address boundary.

The contigmalloc() function will panic if size is zero, or if alignment or boundary is not a power of two.

malloc(9), memguard(9)