Re: [RFC] Optimization for use-once pages

["Stuart MacDonald" <stuartm@connecttech.com>]

From: "Rik van Riel" <riel@conectiva.com.br>
> Actually, the length of this interval could be even smaller
> and is often a point of furious debating.

Which is why I was avoiding flames earlier; I sorta
figured this might be a hot issue.

> Let me give you an example:
>
> - sequential access of a file
> - script reads the file in 80-byte segments
>   (parsing some arcane data structure)
> - these segments are accessed in rapid succession
> - each 80-byte segment is accessed ONCE
>
> In this case, even though the data is accessed only
> once, each page is touched PAGE_SIZE/80 times, with
> one 80-byte read() each time.

I'd figured that sort of scenario was the basis for counting
them all as one. What about

- random access of same file
- script reads one arcane 80 byte struct
- script updates that struct say PAGE_SIZE/80
times, with one 80-byte write() each time

If they're all counted as one, would the page age
correctly, if the script happens to take a few seconds
break between another flurry of all-as-one updating?

..Stu