Standard C Library Functions madvise(3C)
NAME
madvise - provide advice to VM system
SYNOPSIS
#include
#include
int madvise(caddr_t addr, size_t len, int advice);
DESCRIPTION
The madvise() function advises the kernel that a region of
user mapped memory in the range [addr, addr + len) will be accessed following a type of pattern. The kernel uses this information to optimize the procedure for manipulating andmaintaining the resources associated with the specified map-
ping range. Values for advice are defined inas: #define MADV_NORMAL 0x0 /* No further special treatment */
#define MADV_RANDOM 0x1 /* Expect random page references */
#define MADV_SEQUENTIAL 0x2 /* Expect sequential page references */
#define MADV_WILLNEED 0x3 /* Will need these pages */
#define MADV_DONTNEED 0x4 /* Don't need these pages */
#define MADV_FREE 0x5 /* Contents can be freed */
#define MADV_ACCESS_DEFAULT 0x6 /* default access */
#define MADV_ACCESS_LWP 0x7 /* next LWP to access heavily */
#define MADV_ACCESS_MANY 0x8 /* many processes to access heavily */
MADV_NORMAL This is the default system charac-
teristic where accessing memory within the address range causes the system to read data from the mapped file. The kernel reads all data from files into pages which are retained for a period of time as a "cache." System pages can be a scarce resource, so the kernel steals pages from other mappings when needed. This is a likely occurrence, but adversely affects system performance only if a large amount of memory is accessed.MADV_RANDOM Tell the kernel to read in a minimum
amount of data from a mapped file on any single particular access. IfMADV_NORMAL is in effect when an
address of a mapped file is accessed,SunOS 5.11 Last change: 23 Feb 2005 1
Standard C Library Functions madvise(3C)
the system tries to read in as much data from the file as reasonable, in anticipation of other accesses within a certain locality.MADV_SEQUENTIAL Tell the system that addresses in
this range are likely to be accessed only once, so the system will free the resources mapping the address range as quickly as possible.MADV_WILLNEED Tell the system that a certain
address range is definitely needed so the kernel will start reading the specified range into memory. This can benefit programs wanting to minimize the time needed to access memory the first time, as the kernel would need to read in from the file.MADV_DONTNEED Tell the kernel that the specified
address range is no longer needed, so the system starts to free the resources associated with the address range.MADV_FREE Tell the kernel that contents in the
specified address range are no longer important and the range will be overwritten. When there is demand for memory, the system will free pages associated with the specified address range. In this instance, the next time a page in the address range is referenced, it will contain all zeroes. Otherwise, it will contain the data that was there prior to theMADV_FREE call. References made to
the address range will not make the system read from backing store (swap space) until the page is modified again. This value cannot be used on mappings that have underlying file objects.SunOS 5.11 Last change: 23 Feb 2005 2
Standard C Library Functions madvise(3C)
MADV_ACCESS_LWP Tell the kernel that the next LWP to
touch the specified address range will access it most heavily, so the kernel should try to allocate the memory and other resources for this range and the LWP accordingly.MADV_ACCESS_MANY Tell the kernel that many processes
and/or LWPs will access the specified address range randomly across the machine, so the kernel should try to allocate the memory and other resources for this range accordingly.MADV_ACCESS_DEFAULT Reset the kernel's expectation for
how the specified range will be accessed to the default.The madvise() function should be used by applications with
specific knowledge of their access patterns over a memoryobject, such as a mapped file, to increase system perfor-
mance.RETURN VALUES
Upon successful completion, madvise() returns 0; otherwise,
it returns -1 and sets errno to indicate the error.
ERRORS
EAGAIN Some or all mappings in the address range[addr, addr + len) are locked for I/O. EBUSY Some or all of the addresses in the range [addr,
addr + len) are locked and MS_SYNC with the
MS_INVALIDATE option is specified.
EFAULT Some or all of the addresses in the specified range could not be read into memory from theunderlying object when performing MADV_WILLNEED.
The madvise() function could return prior to this
condition being detected, in which case errno will not be set to EFAULT. EINVAL The addr argument is not a multiple of the page size as returned by sysconf(3C), the length of the specified address range is equal to 0, or theSunOS 5.11 Last change: 23 Feb 2005 3
Standard C Library Functions madvise(3C)
advice argument was invalid.EIO An I/O error occurred while reading from or writ-
ing to the file system.ENOMEM Addresses in the range [addr, addr + len) are out-
side the valid range for the address space of a process, or specify one or more pages that are not mapped. ESTALE Stale NFS file handle.ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
meminfo(2), mmap(2), sysconf(3C), attributes(5)SunOS 5.11 Last change: 23 Feb 2005 4