Re: [RFC] Limit the size of the IPV4 route hash.

From: Robin Holt
Date: Fri Dec 10 2004 - 18:29:31 EST

On Fri, Dec 10, 2004 at 01:09:47PM -0800, Andrew Morton wrote:
> Robin Holt <holt@xxxxxxx> wrote:
> > Can we agree that a linear calculation based on num_physpages is probably
> > not the best algorithm. If so, should we make it a linear to a limit or
> > a logarithmically decreasing size to a limit? How do we determine that
> > limit point?
> An initial default of N + M * log2(num_physpages) would probably give a
> saner result.
> The big risk is that someone has a too-small table for some specific
> application and their machine runs more slowly than it should, but they
> never notice. I wonder if it would be possible to put a little once-only
> printk into the routing code: "warning route-cache chain exceeded 100
> entries: consider using the rhash_entries boot option".

Since the hash gets flushed every 10 seconds, what if we kept track of
the maximum depth reached and when we reach a certain threshold, just
allocate a larger hash and replace the old with the new. I do like the
printk idea so the admin can prevent inconsistent performance early in
the run cycle for the system. We could even scale the hash size up based
upon demand.

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