POSIX_MADVISE
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
posix_madvise - give advice about patterns of memory usage
SYNOPSIS
#include <sys/mman.h>
int posix_madvise(void *addr, size_t len, int advice);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
posix_madvise():
-
_POSIX_C_SOURCE >= 200112L
DESCRIPTION
The
posix_madvise()
function allows an application to advise the system about its expected
patterns of usage of memory in the address range starting at
addr
and continuing for
len
bytes.
The system is free to use this advice in order to improve the performance
of memory accesses (or to ignore the advice altogether), but calling
posix_madvise()
shall not affect the semantics of access to memory in the specified range.
The
advice
argument is one of the following:
- POSIX_MADV_NORMAL
-
The application has no special advice regarding its memory usage patterns
for the specified address range.
This is the default behavior.
- POSIX_MADV_SEQUENTIAL
-
The application expects to access the specified address range sequentially,
running from lower addresses to higher addresses.
Hence, pages in this region can be aggressively read ahead,
and may be freed soon after they are accessed.
- POSIX_MADV_RANDOM
-
The application expects to access the specified address range randomly.
Thus, read ahead may be less useful than normally.
- POSIX_MADV_WILLNEED
-
The application expects to access the specified address range
in the near future.
Thus, read ahead may be beneficial.
- POSIX_MADV_DONTNEED
-
The application expects that it will not access the specified address range
in the near future.
RETURN VALUE
On success,
posix_madvise()
returns 0.
On failure, it returns a positive error number.
ERRORS
- EINVAL
-
addr
is not a multiple of the system page size or
len
is negative.
- EINVAL
-
advice
is invalid.
- ENOMEM
-
Addresses in the specified range are partially or completely outside
the caller's address space.
VERSIONS
Support for
posix_madvise()
first appeared in glibc version 2.2.
CONFORMING TO
POSIX.1-2001.
NOTES
POSIX.1 permits an implementation to generate an error if
len
is 0.
On Linux, specifying
len
as 0 is permitted (as a successful no-op).
In glibc, this function is implemented using
madvise(2).
However, since glibc 2.6,
POSIX_MADV_DONTNEED
is treated as a no-op, because the corresponding
madvise(2)
value,
MADV_DONTNEED,
has destructive semantics.
SEE ALSO
madvise(2),
posix_fadvise(2)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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