SYNOPSIS
#include <sys/mman.h>
int posix_madvise(void *addr, size_t len,
int advice);
DESCRIPTION
The posix_madvise() function need only be supported if either the Memory Mapped Files or the Shared Memory Objects options are supported.
The posix_madvise() function shall advise the implementation on the expected behavior of the application with respect to the data in the memory starting at address addr, and continuing for len bytes. The implementation may use this information to optimize handling of the specified data. The posix_madvise() function shall have no effect on the semantics of access to memory in the specified range, although it may affect the performance of access.
The implementation may require that addr be a multiple of the page size, which is the value returned by sysconf() when the name value _SC_PAGESIZE is used.
The advice to be applied to the memory range is specified by the advice parameter and may be one of the following values:
- POSIX_MADV_NORMAL
-
Specifies that the application has no advice to give on its behavior with respect to the specified range. It is the default characteristic if no advice is given for a range of memory.
- POSIX_MADV_SEQUENTIAL
-
Specifies that the application expects to access the specified range sequentially from lower addresses to higher addresses.
- POSIX_MADV_RANDOM
-
Specifies that the application expects to access the specified range in a random order.
- POSIX_MADV_WILLNEED
-
Specifies that the application expects to access the specified range in the near future.
- POSIX_MADV_DONTNEED
-
Specifies that the application expects that it will not access the specified range in the near future.
These values are defined in the <sys/mman.h> header.
RETURN VALUE
Upon successful completion, posix_madvise() shall return zero; otherwise, an error number shall be returned to indicate the error.
ERRORS
The posix_madvise() function shall fail if:
- EINVAL
- The value of advice is invalid.
- ENOMEM
-
Addresses in the range starting at addr and continuing for len
bytes are partly or completely outside the range
allowed for the address space of the calling process.
The posix_madvise() function may fail if:
- EINVAL
- The value of addr is not a multiple of the value returned by sysconf() when the name value _SC_PAGESIZE is used.
- EINVAL
-
The value of len is zero.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The posix_madvise() function is part of the Advisory Information option and need not be provided on all implementations.
RATIONALE
None.
FUTURE DIRECTIONS
None.
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .