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.