Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]

Andrea Arcangeli
2003-02-10T08:47:29Z

On Mon, Feb 10, 2003 at 12:19:21AM -0800, Andrew Morton wrote:
> Andrea Arcangeli <andrea@suse.de> wrote:
> >
> > BTW, one thing that should definitely do readhaead and it's
> > not doing that (at least in 2.4) is the readdir path, again to generate
> > big commands, no matter the seeks. It was lost with the directory in
> > pagecache.
>
> Yes. But ext3 is still doing directory readahead, and I have never
> noticed it gaining any particular benefit over ext2 from it.

At least for big directories it should be at least a quite obvious
microoptimization, if you do it at the logical level. Maybe it wasn't
worthwhile in the past (like in ext3) because it was done at the block
layer with a dumb reada rather than with proper read of the next logical
block before wait_on_buffer. Also keep in mind the max readahead
generated by the block layer is nothing compared to the true readahead
that the logical layer is able to generate.

Andrea