Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

madvise(2) [mojave man page]

MADVISE(2)						      BSD System Calls Manual							MADVISE(2)

NAME
madvise, posix_madvise -- give advice about use of memory SYNOPSIS
#include <sys/mman.h> int madvise(void *addr, size_t len, int advice); int posix_madvise(void *addr, size_t len, int advice); DESCRIPTION
The madvise() system call allows a process that has knowledge of its memory behavior to describe it to the system. The advice passed in may be used by the system to alter its virtual memory paging strategy. This advice may improve application and system performance. The behavior specified in advice can only be one of the following values: MADV_NORMAL Indicates that the application has no advice to give on its behavior in the specified address range. This is the system default behavior. This is used with madvise() system call. POSIX_MADV_NORMAL Same as MADV_NORMAL but used with posix_madvise() system call. MADV_SEQUENTIAL Indicates that the application expects to access this address range in a sequential manner. This is used with madvise() system call. POSIX_MADV_SEQUENTIAL Same as MADV_SEQUENTIAL but used with posix_madvise() system call. MADV_RANDOM Indicates that the application expects to access this address range in a random manner. This is used with madvise() system call. POSIX_MADV_RANDOM Same as MADV_RANDOM but used with posix_madvise() system call. MADV_WILLNEED Indicates that the application expects to access this address range soon. This is used with madvise() system call. POSIX_MADV_WILLNEED Same as MADV_WILLNEED but used with posix_madvise() system call. MADV_DONTNEED Indicates that the application is not expecting to access this address range soon. This is used with madvise() system call. POSIX_MADV_DONTNEED Same as MADV_DONTNEED but used with posix_madvise() system call. MADV_FREE Indicates that the application will not need the information contained in this address range, so the pages may be reused right away. The address range will remain valid. This is used with madvise() system call. MADV_ZERO_WIRED_PAGES Indicates that the application would like the wired pages in this address range to be zeroed out if the address range is deallocated without first unwiring the pages (i.e. a munmap(2) without a preceding munlock(2) or the application quits). This is used with madvise() system call. The posix_madvise() behaves same as madvise() except that it uses values with POSIX_ prefix for the advice system call argument. RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
madvise() fails if one or more of the following are true: [EINVAL] The value of advice is incorrect. [EINVAL] The address range includes unallocated regions. [ENOMEM] The virtual address range specified by the addr and len are outside the range allowed for the address space. LEGACY SYNOPSIS
#include <sys/types.h> #include <sys/mman.h> int madvise(caddr_t addr, size_t len, int advice); int posix_madvise(caddr_t addr, size_t len, int advice); The include file <sys/types.h> is necessary. The type of addr has changed. SEE ALSO
mincore(2), minherit(2), mprotect(2), msync(2), munmap(2), compat(5) HISTORY
The madvise function first appeared in 4.4BSD. The posix_madvise function is part of IEEE 1003.1-2001 and was first implemented in Mac OS X 10.2. BSD
June 9, 1993 BSD

Check Out this Related 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)

Featured Tech Videos