Related to my other bug report today, calling posix_fadvise (which uses
fadvise64) with the POSIX_FADV_NOREUSE flag does nothing.  The pages are
not dropped behind.

I also tried call fadvise with POSIX_FADV_SEQUENTIAL first.

This is expected as the POSIX_FADV_NOREUSE is a no-op in the recent
kernels.

Also, POSIX_FADV_SEQUENTIAL only does the readahead window. It doesn't
hint the VM in any way to possibly drop-behind the pages.

(See the previous bug report for more details of the test case)

Relevant numbers:

Copying (using fadvise_cp) a large file test:

1st run: 0m9.018s
2nd run: 0m3.444s
Copying large file...
3rd run: 0m14.024s    <<< page cache trashed
4th run: 0m3.449s

Test programs and batch files are attached.


- Eric