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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 strat-egy. strategy.
egy. 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() sys-tem system
tem 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 man-ner. manner.
ner. 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 dellocated 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
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