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NetBSD 6.1.5 - man page for madvise (netbsd section 2)

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

     madvise -- give advice about use of memory

     Standard C Library (libc, -lc)

     #include <sys/mman.h>

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

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

     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 priority 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_DONTNEED rather than the flags described above.

     Upon successful completion, a value of 0 is returned.  Otherwise, a value of -1 is returned
     and errno is set to indicate the error.

     madvise() will fail if:

     [EINVAL]		Invalid parameters were provided.

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

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

     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
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