Re: [resent PATCH] Re: very slow parallel read performance

Helge Hafting
2001-08-27T07:10:10Z

Daniel Phillips wrote:
>
> On August 24, 2001 09:02 pm, Rik van Riel wrote:
> > I guess in the long run we should have automatic collapse
> > of the readahead window when we find that readahead window
> > thrashing is going on, in the short term I think it is
> > enough to have the maximum readahead size tunable in /proc,
> > like what is happening in the -ac kernels.
>
> Yes, and the most effective way to detect that the readahead window is too
> high is by keeping a history of recently evicted pages. When we find
> ourselves re-reading pages that were evicted before ever being used we know
> exactly what the problem is.

Counting how much we are reading ahead and comparing with total RAM
(or total cache) might also be an idea. We may then read ahead
a lot for those who runs a handful of processes, and
do smaller readahead for those that runs thousands of processes.

Helge Hafting