[coyotos-dev] Contrasting Coyotos, EROS & Keykos
norm at cap-lore.com
Fri Jan 21 20:09:24 EST 2005
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
> 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
> 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
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
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.
Keykos programmers did not typically assume that their entire address
was kept by one segment keeper.
In Keykos terminology, a segment is either a page or is composed
(typically smaller) segments.
Thus the page passing trick can apply to entire segments with about the
same overhead and without faults for each page.
With a physical cache the data within the transmitted segment remains
in the cache. This is true of all of the proposals.
Norm Hardy: <http://cap-lore.com>
Nothing has an uglier look to us than reason, when it is not on our
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