Re: self-paging

[Marcus Brinkmann]

At Wed, 30 Nov 2005 11:56:29 +0100,
Bas Wijnen <address@hidden> wrote:
> Hm, we have a slightly different definition then.  What I call self-paging is
> that the application itself determines which page will be discarded or swapped
> out on memory pressure.  Informing the application is one way to do that, but
> it can be done differently (as in my proposal, the application just builds a
> prioritized list of pages, and the swapping out and discarding happens without
> notification).

When I proposed something similar to Neal, he said that it may be
important that the application _knows_ about how much memory is going
away, so it can calculate for that.  It makes sense to me.  For
example, a (soft) real time renderer could switch to a lower
resolution, or a stream compressor could use a less memory intensive
algorithm, both to avoid trashing.

> What is essential to self-paging in my view is that the
> decision which page to swap out is made locally, not that that is done at the
> moment there is pressure (that is, in my proposal the decision is prepared
> beforehand and used by the system when needed).

EROS has the concept of working sets with priorities.  This gives
advice to the paging system how you group your memory pages.

Maybe the term "advisory page mechanism" (or something like that) is
better to describe your idea rather than self-paging.  In particular,
you said in your original mail that the system swaps out pages.  This
is one indication that what you describe is not really self-paging.

It seems to me that apart from this difference, your proposal boils
down to: "Add noise to the system to reduce the bandwidth of covert
channels", which is the typical approach if all else fails.

Thanks,
Marcus