[coyotos-dev] Contrasting Coyotos, EROS & Keykos

Jonathan S. Shapiro shap at eros-os.org
Sat Jan 22 00:46:25 EST 2005

On Fri, 2005-01-21 at 17:09 -0800, Norman Hardy wrote:
> On Jan 21, 2005, at 12:06 PM, Jonathan S. Shapiro wrote:
> > A strange thought occurred to me at some point last night.
> >
> > One of the things we would like to be able to do in certain 
> > applications
> > is something like "page flipping", where process A can send a page that
> > process B will populate. The idea being to avoid copying the data 
> > during
> > IPC.
> >
> > This was possible in EROS/KeyKOS, but inconvenient because it required
> > traversing the mapping structures explicitly.
> A Keykos application with this need would probably arrange static 
> access to
> a node in the memory tree and a reserved slot in that node.
> This arrangement required some knowledge of the memory tree logic.
> Storing into the slot caused the kernel to execute a few hundred 
> instructions
> to kill the part of the real map defined by the previous slot contents,
> and perhaps  a few hundred more to enable the new access.

Yes, this can certainly be done, and for mapping a single page (up to 3,
actually) it would work fine, but it doesn't generalize well to larger


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