text: NAME
  msync -- synchronize a mapped region
  LIBRARY
  Standard C Library (libc, -lc)
  SYNOPSIS
  #include <sys/mman.h> int msync(void *addr, size_t len, int flags);
  DESCRIPTION
  The msync() system call writes any modified pages back to the file system and updates the file modification time. If len is 0, all modified pages within the region containing addr will be flushed; if len is non-zero, only those pages containing addr and len-1 succeeding locations will be examined. The flags argument may be specified as follows: MS_ASYNC Return immediately MS_SYNC Perform synchronous writes MS_INVALIDATE Invalidate all cached data
  RETURN. [EINVAL] The len argument is too large or negative. [EINVAL] The flags argument was both MS_ASYNC and MS_INVALIDATE. Only one of these flags is allowed.
  SEE ALSO
  madvise(2), mincore(2), mlock(2), mprotect(2), munmap(2)
  HISTORY
  The msync() system call first appeared in 4.4BSD.
  BUGS
  The msync() system call is obsolete since BSD implements a coherent file system buffer cache. However, it may be used to associate dirty VM pages with file system buffers and thus cause them to be flushed to physical media sooner rather than later.