We discussed adding this facility to KeyKOS. We all thought it was a good idea. I would add to your list of outcomes, traversal depth limit reached (to avoid long units of operation).
At 1:59 PM -0800 11/12/97, Jonathan Shapiro wrote:
>I cannot recall if I proposed this before.
>
>On grounds of the performance importance of memory fault resolution, I am
>debating the introduction of two new operations on nodes, tentatively called
>"fetch" and "store". These expose the memory tree walking functionality
>already implemented by the kernel to allow the holder of a node capability
>to store a capability in a slot by walking a memory-address style path
>through a node tree, or similarly to fetch a capability from such a slot.
>The arguments are:
>
> address (i.e. path through tree)
> target lss (of node containing slot to be revised)
> capability to store (store only)
>
>Likely users of this service are memory keepers and supernode-like programs.
>
>The walk would preserve all current protections and restrictions, including
>the requirement that it not cross a segment key (though crossing a window
>would appear to be okay). It is merely a way to collapse the many
>capability invocations currently used to walk the tree into a single call,
>thereby avoiding kernel/user crossings. It does not appear to require any
>significant amount of new code; the address resolver used by the TLB miss
>handler already produces all of the required information.
>
>Possible outcomes of such a call are:
>
> success
> insufficient permission (somewhere on path, where is unspecified)
> invalid address (somewhere on path, where is unspecified)
> malformed segtree
>
>Does anyone see a reason in principle why such an addition might not be
>correct?
>
>Does anyone see another argument of principle about why this should not be
>done?
>
>Separate from arguments of principle, does anyone wish to suggest a reason
>not to do this?
>
>
>shap
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