Re: VM Requirement Document - v0.0

From: Daniel Phillips (
Date: Thu Jun 28 2001 - 11:02:58 EST

On Thursday 28 June 2001 17:21, Jonathan Morton wrote:
> >There is a simple change in strategy that will fix up the updatedb case
> > quite nicely, it goes something like this: a single access to a page
> > (e.g., reading it) isn't enough to bring it to the front of the LRU
> > queue, but accessing it twice or more is. This is being looked at.
> Say, when a page is created due to a page fault, page->age is set to
> zero instead of whatever it is now.

This isn't quite enough. We do want to be able to assign a ranking to
members of the accessed-once set, and we do want to distinguish between newly
created pages and pages that have aged all the way to zero.

> Then, on the first access, it is
> incremented to one. All accesses where page->age was previously zero
> cause it to be incremented to one, and subsequent accesses where
> page->age is non-zero cause a doubling rather than an increment.
> This gives a nice heavy priority boost to frequently-accessed pages...

While on that topic, could somebody please explain to me why exponential
aging is better than linear aging by a suitably chosen increment? It's clear
what's wrong with it: after 32 hits you lose all further information. I
suspect there are more problems with it than that.

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This archive was generated by hypermail 2b29 : Sat Jun 30 2001 - 21:00:19 EST