Re: [RFC] - Some notions that I would like comments on

Jamie Lokier (lkd@tantalophile.demon.co.uk)
Wed, 14 Jul 1999 21:56:38 +0200

Stephen C. Tweedie wrote:
> > We don't do it on mmaped areas yet though.
>
> In 2.2, we do --- sort of. We "readaround", instead --- we page in an
> entire contiguuous 64k-long, 64k-aligned chunk of the file by default
> (less on low-memory machines).
>
> In conjunction with the disk track buffer, this has the effect of
> readahead if you are accessing a mmaped file sequentially in memory ---
> on 2.2, programs which use mmap (such as grep) will happily run at disk
> speed now. The readaround algorithm has the advantage over readahead
> that it also works very well when randomly paging in executable files
> (this is why netscape loads 2 to 3 times faster on 2.2 than on 2.0 on my
> machines).

Does this completely avoid blocking then?

I mean, is "readaround" for block @ 128k-192k triggered by
reading/paging within block @ 64k-128k, or is it triggered by the first
read with 128k-192k?

thanks,
-- Jamie

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