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 advice);
int
posix_madvise(void *addr, size_t len, int advice);

DESCRIPTION
The madvise() system call allows a process that has knowledge of its memory behavior to describe it to the system. The advice passed in may be used by the system to alter its virtual memory paging strategy. This advice may improve application and system performance. The behavior specified in advice can only be one of the following values:

MADV_NORMAL
    Indicates that the application has no advice to give on its behavior in the specified address range. This is the system default behavior. This is used with madvise() system call.

POSIX_MADV_NORMAL
    Same as MADV_NORMAL but used with posix_madvise() system call.

MADV_SEQUENTIAL
    Indicates that the application expects to access this address range in a sequential manner. This is used with madvise() system call.

POSIX_MADV_SEQUENTIAL
    Same as MADV_SEQUENTIAL but used with posix_madvise() system call.

MADV_RANDOM
    Indicates that the application expects to access this address range in a random manner. This is used with madvise() system call.

POSIX_MADV_RANDOM
    Same as MADV_RANDOM but used with posix_madvise() system call.

MADV_WILLNEED
    Indicates that the application expects to access this address range soon. This is used with madvise() system call.

POSIX_MADV_WILLNEED
    Same as MADV_WILLNEED but used with posix_madvise() system call.

MADV_DONTNEED
    Indicates that the application is not expecting to access this address range soon. This is used with madvise() system call.

POSIX_MADV_DONTNEED
    Same as MADV_DONTNEED but used with posix_madvise() system call.

MADV_FREE
    Indicates that the application will not need the information contained in this address range, so the pages may be reused right away. The address range will remain valid. This is used with madvise() system call.

MADV_ZERO_WIRED_PAGES
    Indicates that the application would like the wired pages in this address range to be zeroed out if the address range is deallocated without first unwiring the pages (i.e. a munmap(2) without a preceding munlock(2) or the application quits). This is used with madvise() system call.

The posix_madvise() behaves same as madvise() except that it uses values with POSIX_ prefix for the advice system call argument.

RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS
madvise() fails if one or more of the following are true:

[EINVAL]
    The value of advice is incorrect.

[EINVAL]
    The address range includes unallocated regions.

[ENOMEM]
    The virtual address range specified by the addr and len are outside the range allowed for the address space.

LEGACY SYNOPSIS
#include <sys/types.h> #include <sys/mman.h>

int
madvise(caddr_t addr, size_t len, int advice);

int
posix_madvise(caddr_t addr, size_t len, int advice);

The include file <sys/types.h> is necessary. The type of addr has changed.

SEE ALSO
mincore(2), minherit(2), mprotect(2), msync(2), munmap(2), compat(5)

HISTORY
The madvise function first appeared in 4.4BSD. The posix_madvise function is part of IEEE 1003.1-2001 and was first implemented in Mac OS X 10.2.