Visit Our UNIX and Linux User Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #491
Difficulty: Easy
In general, interpreted languages are slower than compiled languages.
True or False?
Linux & Unix Commands - Search Man Pages

posix_madvise(3) [bsd man page]

POSIX_MADVISE(3)					     Linux Programmer's Manual						  POSIX_MADVISE(3)

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 speci- fied 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 4.15 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 2017-09-15 POSIX_MADVISE(3)

Check Out this Related Man Page

posix_madvise(3C)					   Standard C Library Functions 					 posix_madvise(3C)

NAME
posix_madvise - memory advisory information SYNOPSIS
#include <sys/mman.h> int posix_madvise(void *addr, size_t len, int advice); DESCRIPTION
The posix_madvise() function advises the system 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 system may use this information to optimize handling of the specified data. The posix_madvise() function has no effect on the semantics of access to memory in the specified range, although it may affect the performance of access. 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 <sys/mman.h> RETURN VALUES
Upon successful completion, posix_madvise() returns zero. Otherwise, an error number is returned to indicate the error. ERRORS
The posix_madvise() function will 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 len is zero. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
mmap(2), madvise(3C), posix_madvise(3C), attributes(5), standards(5) SunOS 5.11 14 Jul 2008 posix_madvise(3C)

Featured Tech Videos