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, vm_paddr_t 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 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().

IMPLEMENTATION NOTES

       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 contigfree() function does not accept NULL as an address input, unlike free(9).

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

       malloc(9), memguard(9)

Debian                                          January 29, 2015                                 CONTIGMALLOC(9)