Re: VM Requirement Document - v0.0

[Jonathan Morton]

>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.  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...

>Note that we don't actually use a LRU queue, we use a more efficient
>approximation called aging, so the above is not a recipe for implementation.

Maybe it is, but in a slightly lateral manner as above.

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