Re: on load control / process swapping

[Roger Larsson <roger.larsson@norran.net>]

On Tuesday 15 May 2001 19:24, Matt Dillon wrote:
>     I implemented a special page-recycling algorithm in 4.1/4.2 (which is
>     still there in 4.3).  Basically it tries predict when it is possible to
>     throw away pages 'behind' a sequentially accessed file, so as not to
>     allow that file to blow away your cache.  E.G. if you have 128M of ram
>     and you are sequentially accessing a 200MB file, obviously there is
>     not much point in trying to cache the data as you read it.
>
>     But being able to predict something like this is extremely difficult.
>     In fact, nearly impossible.  And without being able to make the
>     prediction accurately you simply cannot determine how much data you
>     should try to cache before you begin recycling it.  I wound up having
>     to change the algorithm to act more like a heuristic -- it does a rough
>     prediction but doesn't hold the system to it, then allows the page
>     priority mechanism to refine the prediction.  But it can take several
>     passes (or non-passes) on the file before the page recycling
> stabilizes.
>

Are the heuristics persistent? 
Or will the first use after  boot use the rough prediction? 
For how long time will the heuristic stick? Suppose it is suddenly used in
a slightly different way. Like two sequential readers instead of one...

/RogerL

-- 
Roger Larsson
Skelleftea
Sweden

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