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

Daniel Phillips
2001-08-25T00:36:56Z

On August 25, 2001 01:10 am, Rik van Riel wrote:
> On Sat, 25 Aug 2001, 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,
> >
> > Yes, and the most effective way to detect that the readahead
> > window is too high is by keeping a history of recently evicted
> > pages.
>
> I think it could be even easier. We simply count for each
> file how many pages we read-ahead and how many pages we
> read.
>
> If the number of pages being read-ahead is really a lot
> higher than the pages being read, we know pages get evicted
> before we read them ==> we shrink the readahead window.
>
> This simpler scheme should also be able to correctly set
> the readahead window for slower data streams to smaller
> than the readahead window size for faster reading data
> streams (which _do_ get to use more of their data before
> it is evicted again).

Yes, this is a good method.

--
Daniel