MADVISE(2)

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

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 prot argument is invalid or the specified address range would wrap around.

[EPERM]
    The addr and len parameters specify a region which contains at least one page marked immutable.

[EFAULT]
    For the MADV_FREE operation, the addr and len parameters specify a region which contains at least one page which is not PROT_WRITE.

SEE ALSO
minherit(2), mprotect(2), msync(2), munmap(2)

STANDARDS
The posix_madvise() system call conforms to p1003.1-2008.

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.