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POSIX_MADVISE
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
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PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
posix_madvise - memory advisory information and alignment control
(ADVANCED REALTIME)
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.
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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