Re: [RFC][PATCH] on-demand readahead

Andi Kleen
2007-04-25T13:39:52Z

Fengguang Wu <fengguang.wu@gmail.com> writes:

> OVERHEADS
>
> The new code reduced the overheads of
>
> - excessively calling the readahead routine on small sized reads
> (the current readahead code insists on seeing all requests)
>
> - doing a lot of pointless page-cache lookups for small cached files
> (the current readahead only turns itself off after 256 cache hits,
> unfortunately most files are < 1MB, so never see that chance)

Would it make sense to keep track in the AS if the file is completely in cache?
Then you could probably avoid a lot of these lookups for small in cache files

> --- linux-2.6.21-rc7-mm1.orig/mm/readahead.c
> +++ linux-2.6.21-rc7-mm1/mm/readahead.c
> @@ -733,6 +733,11 @@ unsigned long max_sane_readahead(unsigne

Quite simple patch, why is it that much simpler than your earlier patchkits?
Or is that on top of them?

You seem to have a lot of magic numbers. They probably all need symbols and
explanations.

Your white space also needs some work.

-Andi