Provided by: freebsd-manpages_7.2-1_all
contigmalloc, contigfree - manage contiguous kernel physical memory
contigmalloc(unsigned long size, struct malloc_type *type, int flags,
vm_paddr_t low, vm_paddr_t high, unsigned long alignment,
unsigned long boundary);
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.
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
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
The contigmalloc() function returns a kernel virtual address if
allocation succeeds, or NULL otherwise.
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.