Re: 2.1.113 Mill I 8MB & scrollback :-(

Geert Uytterhoeven (Geert.Uytterhoeven@cs.kuleuven.ac.be)
Thu, 6 Aug 1998 16:39:26 +0200 (CEST)

On Thu, 6 Aug 1998, Jeff Noxon wrote:
> On Wed, Aug 05, 1998 at 11:29:16PM +0200, Geert Uytterhoeven wrote:
> > That's normal. Scrollback doesn't work on frame buffer devices unless you have
> > a virtual screen that's larger than your visible screen.
> >
> > Vesafb doesn't support a virtual screen. Some other frame buffer devices for
> > non-Intel architectures do.
>
> Let me ask a dumb question:
>
> Why does scrollback rely on video memory? It's horribly limiting.

Yes it is. But that's the easy way, for both vgacon and fbcon:

- vgacon implements scrolling (and scrollback) by panning the VGA text screen
- fbcon implements scrolling (and scrollback) by panning the graphical screen
image

In both drivers, scrolling is accelerated by using panning (if possible), and
you get the scrollback buffer for free.

> I'd love to have (or be able to configure) scrollback to come from kernel
> memory instead. That way I could choose to have a 1MB scrollback buffer
> if I wanted... And it would be 1MB of actual *text*, even in the case of
> a graphical console.

That would be valuable unswappable kernel memory. Unused video memory is
available for free.

And your next question will be: why not implement scrollback for all VCs, not
only for the current VC? Because it will consume even more valuable unswappable
kernel memory.

Greetings,

Geert

--
Geert Uytterhoeven                     Geert.Uytterhoeven@cs.kuleuven.ac.be
Wavelets, Linux/{m68k~Amiga,PPC~CHRP}  http://www.cs.kuleuven.ac.be/~geert/
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium




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