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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
POSIX_MADVISE(3) Linux Programmer's Manual POSIX_MADVISE(3)
posix_madvise - give advice about patterns of memory usage
#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
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.
On success, posix_madvise() returns 0. On failure, it returns a
positive error number.
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.
Support for posix_madvise() first appeared in glibc version 2.2.
POSIX.1-2001.
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.
madvise(2), posix_fadvise(2)
This page is part of release 4.12 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/.
Linux 2017-07-13 POSIX_MADVISE(3)
Pages that refer to this page: madvise(2), mincore(2), posix_fadvise(2)