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 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.

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)