Re: (XFree86) mmap of /proc/XXX/mem

Egbert Eich (eich@hilbert.ikp.physik.tu-darmstadt.de)
Thu, 2 Dec 1999 09:20:44 +0100 (MET)

Alexander Viro writes:
>
>
> On Thu, 2 Dec 1999, Egbert Eich wrote:
>
> > Yes, but how? We need a solution otherwise we won't be able to
> > use the vm86 mode even on Intel. The emulator makes everything
> > even slower.
>
> Check dosemu. The _real_ problem with /proc/<pid>/mem is that it needs
> very different behaviour in different parts of process address space. Just
> aliasing every page and hoping that extra reference will save your day is
> _very_ bad idea - behaviour of pages on swapout, etc. is determined by
> vma, not by reference in page table. We _might_ go for /proc/<pid>/object/
> a-la Slowlaris, and that might be made mmap'able, but that's a separate
> story. And IMO an overkill.
>
> Dosemu does aliasing in very similar situation. Check how it's done.

I don't think dosemu saves my day. It needs just _one_ 1Mb real mode image.
I know how to do that, too. No problem. As I tried to explain in
my original posting I need _several_ 1Mb images: one for each graphics
card. I need to swap them _fast_ without moving around large
chunks of memory.
When another card is selected I could in prinicple copy out the
1 Meg image of the one previously selected and then copy in the
1 Meg of the newly selected one. But this is _slow_ compared to
just calling munmap()/mmap() to swap cards. If I only did that
for initialization it's OK. But if I want to do it while the Xserver
is running and in Operating state (ie for updating pallete or
whatever else needs to be done) it is painfully slow.
With mmap() /proc/XXX/mem I can keep all images set up in virtual
address space and only map in the one I need.

Regards,
Egbert.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/