---
name: "madvise"
section: "2"
platform: "macos"
package: "xnu"
version: "12377.121.6"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/madvise"
---

# madvise(2)

give advice about use of memory

## 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)](/munmap/2.md) without a preceding [munlock(2)](/munlock/2.md) 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)](/mincore/2.md), [minherit(2)](/minherit/2.md), [mprotect(2)](/mprotect/2.md), [msync(2)](/msync/2.md), [munmap(2)](/munmap/2.md), [compat(5)](/compat/5.md)

## 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.