CONTIGMALLOC(9)

NAME
contigmalloc, contigfree - manage contiguous kernel physical memory

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

DESCRIPTION
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 type argument is ignored.

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

M_WAITOK
    Causes contigmalloc() to try flushing the active page queue in its second pass. Note that (unlike kmalloc(M_WAITOK)) contigmalloc(M_WAITOK) can still return NULL.

M_ZERO
    Causes the allocated physical memory to be zero filled.

Other flags (if present) are ignored.

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

IMPLEMENTATION NOTES
The contigmalloc() function does not sleep waiting for memory resources to be freed up, but instead scans available physical memory a small number of times for a suitably sized free address range before giving up. Memory allocation is done on a first-fit basis, starting from the top of the provided address range.

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

EXAMPLES

    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.

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

SEE ALSO
kmalloc(9)