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.
SEE ALSO
STANDARDS
The posix_madvise() system call conforms
to IEEE Std 1003.1-2008
(“POSIX.1”).
HISTORY
The madvise() function first appeared in
4.4BSD. 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.