CONTIGMALLOC(9) BSD Kernel Developer's Manual 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 num‐
ber 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 alloca‐
tion 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 cross‐
ing 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 ALSOkmalloc(9)BSD January 19, 2008 BSD
