Using madvise()

The madvise() function advises the kernel that a region of user virtual memory in the range starting at the address specified in addr and with length equal to the value of the len parameter is expected to follow a particular pattern of use. The kernel uses this information to optimize the procedure for manipulating and maintaining the resources associated with the specified range. Use of the madvise() function can increase system performance when used by programs that have specific knowledge of their access patterns over memory.

#include <sys/types.h>
#include <sys/mman.h>
int madvise(caddr_t addr, size_t len, int advice);

The madvise() function provides the following flags to affect how a thread's memory is allocated among lgroups:

MADV_ACCESS_DEFAULT

This flag resets the kernel's expected access pattern for the specified range to the default.

MADV_ACCESS_LWP

This flag advises the kernel that the next LWP to touch the specified address range is the LWP that accesses the range the most. The kernel allocates the memory and other resources for this range and the LWP accordingly.

MADV_ACCESS_MANY

This flag advises the kernel that many processes or LWPs will access the specified address range randomly across the system. The kernel allocates the memory and other resources for this range accordingly.

The madvise() function can return the following values:

EAGAIN

Some or all of the mappings in the specified address range, from addr to addr+len, are locked for I/O.

EINVAL

The value of the addr parameter is not a multiple of the page size as returned by sysconf() function, the length of the specified address range is less than or equal to zero, or the advice is invalid. For more information, see the sysconf(3C) man page.

EIO

An I/O error occurs while reading from or writing to the file system.

ENOMEM

Addresses in the specified range are outside the valid range for the address space of a process or the addresses in the specified range specify one or more pages that are not mapped.

ESTALE

The NFS file handle is stale.