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POSIX_MADVISE(P) POSIX_MADVISE(P)
NAME
posix_madvise - memory advisory information and alignment control (ADVANCED REAL-
TIME)
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 behav-
ior 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 sequen-
tially 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.
SEE ALSO
mmap() , posix_fadvise() , sysconf() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/mman.h>
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 .
POSIX 2003 POSIX_MADVISE(P)
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