better perf and memory uage for xfs_fsr? Trivial patch against xfstools-3.16 included...

[Linda Walsh]

FWIW, the benefit, probably comes from the read-file, as the written file
is written with DIRECT I/O and I can't see that it should make a difference
there.

Another thing I noted -- when xfs_fsr _exits_, ALL of the space it had used
for file cache read into memory -- gets freed - whereas before, it just stayed in
the buffer cache and didn't get released until the space was needed.

Linda Walsh wrote:
> I wondered why it lumped all this memory reclaiming and thought to try 
> using
> the posix_fadvise calls in xfs_fsr to tell the kernel what data was 
> unneeded
> and such...