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 mem‐
ory 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() sys‐
tem 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() sys‐
tem call.
MADV_FREE Indicates that the application will not need the infor‐
mation 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.
ERRORSmadvise() 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 ALSOmincore(2), minherit(2), mprotect(2), msync(2), munmap(2), compat(5)HISTORY
The madvise function first appeared in 4.4BSD. The posix_madvise func‐
tion is part of IEEE 1003.1-2001 and was first implemented in Mac OS X
10.2.
BSD June 9, 1993 BSD
