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.

MADV_ZERO

Indicates that the application would like this address range effectively zeroed without causing unnecessary memory accesses. This could return ENOTSUP in some situations, in which case the caller should fall back to zeroing the range themselves. 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.

[EPERM]

The operation isn't allowed on a part (or whole) of the address range due to restrictions.

[ENOTSUP]

The operation is not supported.

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.