posix_madvise

- memory advisory information

Synopsis

#include <sys/mman.h>

int posix_madvise(void *addr, size_t len, int advice);

Description

The posix_madvise() function advises the system on the expected behavior of the application with respect to the data in the memory starting at address addr, and continuing for len bytes. The system may use this information to optimize handling of the specified data. The posix_madvise() function has no effect on the semantics of access to memory in the specified range, although it may affect the performance of access.

The advice to be applied to the memory range is specified by the advice parameter and may be one of the following values:

POSIX_MADV_NORMAL

Specifies that the application has no advice to give on its behavior with respect to the specified range. It is the default characteristic if no advice is given for a range of memory.

POSIX_MADV_SEQUENTIAL

Specifies that the application expects to access the specified range sequentially from lower addresses to higher addresses.

POSIX_MADV_RANDOM

Specifies that the application expects to access the specified range in a random order.

POSIX_MADV_WILLNEED

Specifies that the application expects to access the specified range in the near future.

POSIX_MADV_DONTNEED

Specifies that the application expects that it will not access the specified range in the near future.

These values are defined in <sys/mman.h>

Return Values

Upon successful completion, posix_madvise() returns zero. Otherwise, an error number is returned to indicate the error.

Errors

The posix_madvise() function will fail if:

EINVAL

The value of advice is invalid.

ENOMEM

Addresses in the range starting at addr and continuing for len bytes are partly or completely outside the range allowed for the address space of the calling process.

The posix_madvise() function may fail if:

EINVAL

The value of len is zero.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

mmap(2), madvise(3C), posix_madvise(3C), attributes(5), standards(5)