Re: [RFC] kernel facilities for cache prefetching

[Wu Fengguang]

On Tue, May 02, 2006 at 10:09:36AM +0200, Jens Axboe wrote:
> I tried something very similar to this years ago, except I made it
> explicit instead of hiding it in the blk_run_backing_dev() which we
> didn't have at that time. My initial results showed that you would get a
> load of requests for different pages so would end up doing io randomly
> instead again.

Yes, the hard one would be _not_ to impact normal I/Os in any way.
A simple solution for the case of deadline scheduler would be:

- static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
+ static const int read_expire = HZ / 2;  /* max time before a impending read is submitted. */
+ static const int reada_expire = HZ * 30;  /* max time before a read-ahead is submitted. */

Wu
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