posix_madvise(2) [netbsd man page]

MADVISE(2)						      BSD System Calls Manual							MADVISE(2)

NAME

     madvise -- give advice about use of memory

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/mman.h>

     int
     madvise(void *addr, size_t len, int behav);

     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 posix_madvise()
     interface is identical and is provided for standards conformance.

     The known behaviors are:

     MADV_NORMAL      Tells the system to revert to the default paging behavior.

     MADV_RANDOM      Is a hint that pages will be accessed randomly, and prefetching is likely not advantageous.

     MADV_SEQUENTIAL  Is a hint that pages will be accessed sequentially, from the lower address to higher address.  It might cause the VM system
		      to depress the priority of pages immediately preceding a given page when it is faulted in.

     MADV_WILLNEED    Is a hint that pages will be accessed in the near future.  It might cause the VM system to make pages that are in a given
		      virtual address range to temporarily have higher priority, and if they are in memory, decrease the likelihood of them being
		      freed.  It might immediately map the pages that are already in memory into the process, thereby eliminating unnecessary
		      overhead of going through the entire process of faulting the pages in.  It might or might not fault pages in from backing
		      store.

     MADV_DONTNEED    Is a hint that pages will not be accessed in the near future.  It might allow the VM system to decrease the in-memory prior-
		      ity of pages in the specified range.

     MADV_FREE	      Gives the VM system the freedom to free pages, and tells the system that information in the specified page range is no
		      longer important.

     Portable programs that call the posix_madvise() interface should use the aliases POSIX_MADV_NORMAL, POSIX_MADV_SEQUENTIAL, POSIX_MADV_RANDOM,
     POSIX_MADV_WILLNEED, and POSIX_MADV_DONTNEED rather than the flags described above.

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() will fail if:

     [EINVAL]		Invalid parameters were provided.

SEE ALSO

     mincore(2), mprotect(2), msync(2), munmap(2), posix_fadvise(2)

STANDARDS

     The posix_madvise() system call is expected to conform to the IEEE Std 1003.1-2001 (``POSIX.1'') standard.

HISTORY

     The madvise system call first appeared in 4.4BSD, but until NetBSD 1.5 it did not perform any of the requests on, or change any behavior of
     the address range given.  The posix_madvise() was invented in NetBSD 5.0.

BSD
								  March 29, 2011							       BSD

MADVISE(2)						      BSD System Calls Manual							MADVISE(2)

NAME

     madvise -- give advice about use of memory

SYNOPSIS

     #include <sys/types.h>
     #include <sys/mman.h>

     int
     madvise(caddr_t addr, size_t len, int behav);

     int
     posix_madvise(caddr_t addr, size_t len, int behav);

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 behav can only be one of the following values:

     MADV_NORMAL      Indicates that the application has no advice to give on its behavior in the specifed 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() sys-
		      tem 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.

     The posix_madvise() behaves same as madvise() except that it uses values with POSIX_ prefix for the behav 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 behav is incorrect.

     [ENOMEM]		The virtual address range specified by the addr and len are outside the range allowed for the address space.

     [EINVAL]		The address range includes unallocated regions.

SEE ALSO

     mincore(2), minherit(2), mprotect(2), msync(2), munmap(2)

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.

BSD
								   June 9, 1993 							       BSD