NAME
madvise,
posix_madvise —
give advice about use of
memory
SYNOPSIS
#include
<sys/mman.h>
int
madvise(void
*addr, size_t len,
int behav);
int
posix_madvise(void
*addr, size_t len,
int behav);
DESCRIPTION
The
madvise()
system call allows a process that has knowledge of its memory behavior to
describe it to the system. The posix_madvise()
interface has the same effect, but returns the error value instead of only
setting errno.
The possible behaviors are:
MADV_NORMAL- No further special treatment needed.
MADV_RANDOM- Expect random page access patterns.
MADV_SEQUENTIAL- Expect sequential page references.
MADV_WILLNEED- The pages will be referenced soon.
MADV_DONTNEED- The pages will not be referenced soon.
MADV_SPACEAVAIL- Ensure that resources are reserved.
MADV_FREE- The pages don't contain any useful data and can be recycled.
Portable programs that call the
posix_madvise()
interface should use the aliases POSIX_MADV_NORMAL,
POSIX_MADV_RANDOM,
POSIX_MADV_SEQUENTIAL,
POSIX_MADV_WILLNEED, and
POSIX_MADV_DONTNEED rather than the flags described
above.
RETURN VALUES
The madvise() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate the
error.
If successful, the posix_madvise()
function will return zero. Otherwise an error number will be returned to
indicate the error.
ERRORS
madvise() will fail if:
- [
EINVAL] - The specified behav argument was invalid.
- [
EINVAL] - The addr parameter was not page aligned or addr and size specify a region that would extend beyond the end of the address space.
- [
EPERM] - The addr and len parameters specify a region which contains at least one page marked immutable.
SEE ALSO
mimmutable(2), minherit(2), mprotect(2), msync(2), munmap(2)
STANDARDS
The posix_madvise() system call conforms
to IEEE Std 1003.1-2008
(“POSIX.1”).
The EPERM failure conditions described are
an extension to this specification.
HISTORY
The madvise() function first appeared in
SunOS 4.0 and has been available since OpenBSD 2.7.
The posix_madvise() function first appeared in
OpenBSD 4.8.
BUGS
The MADV_WILLNEED behavior is ignored. The
MADV_SPACEAVAIL behavior is not implemented and will
always fail.