MADVISE(2)                NetBSD System Calls Manual                MADVISE(2)

madvise -- give advice about use of memory
Standard C Library (libc, -lc)
#include <sys/mman.h> int madvise(void *addr, size_t len, int behav); int posix_madvise(void *addr, size_t len, int advice);
The madvise() system call allows a process that has knowledge of its mem- ory 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 Causes the VM system to depress the priority of pages imme- diately preceding a given page when it is faulted in. MADV_WILLNEED Causes 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. Additionally, the pages that are already in memory will be immediately mapped into the process, thereby eliminating unnecessary overhead of going through the entire process of faulting the pages in. This WILL NOT fault pages in from backing store, but quickly map the pages already in memory into the calling process. MADV_DONTNEED Allows the VM system to decrease the in-memory priority of pages in the specified range. Additionally future refer- ences to this address range will incur a page fault. 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.
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. NetBSD 5.0_RC4 April 19, 2008 NetBSD 5.0_RC4

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