readdir request re-requests entries

["Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>]

Dear NFS fellows,

we have notice a behavior of nfs client when iterating over a big
directory. The client re-requests entries that already has been. For
example, a client issues READDIR on a directory with 1k files. Initial cookie
is 0, maxcount 32768.

c -> s cookie 0
s -> c last cookie 159
c -> s cookie 105
s -> c last cookie 259
c -> s cookie 207

...

and so on. The interesting thing is, if I mount with rsize 8192 (maxcount 8192), then first couple
or requests are asking for correct cookies - 0, 43, 81, 105. Again 105 as with maxcount 32678. To
me it looks like that there is some kind of internal page (actually NFS_MAX_READDIR_PAGES) alignment
and entries which do not fit into initially allocated PAGE_SIZE * NFS_MAX_READDIR_PAGES memory
just get dropped.

As 30% of each reply is thrown away, listing of large directories may produce much more requests
than required.

Is it an expected behavior?

Thanks in advance,
   Tigran.