posix_madvise

Section: C Library Functions (3)
Updated: 202-0-08
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NAME

posix_madvise - give advice about patterns of memory usage  

LIBRARY

Standard C library (libc,~-lc)  

SYNOPSIS

#include <sys/mman.h>
int posix_madvise(size_t size;
                  void addr[size], size_t size, 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 size 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 size is negative.

EINVAL

advice is invalid.

ENOMEM

Addresses in the specified range are partially or completely outside the caller's address space.

 

VERSIONS

POSIX.1 permits an implementation to generate an error if size is 0. On Linux, specifying size as 0 is permitted (as a successful n-op). In glibc, this function is implemented using madvise(2). However, since glibc 2.6, POSIX_MADV_DONTNEED is treated as a n-op, because the corresponding madvise(2) value, MADV_DONTNEED, has destructive semantics.  

STANDARDS

POSIX.-2008.  

HISTORY

glibc 2.2. POSIX.-2001.  

SEE ALSO

madvise(2), posix_fadvise(2)

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Index

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

VERSIONS

STANDARDS

HISTORY

SEE ALSO