Re: increasing page size

[Rik van Riel <H.H.vanRiel@phys.uu.nl>]

On Sun, 5 Jul 1998, Gerard Roudier wrote:
> On Sun, 5 Jul 1998, Rik van Riel wrote:
> 
> > Even if files are fragmented, readahead _will_ give a large
> > performance increase. This is because we can bring in the
> 
> This requires:
> 
> 1 - The program will really need the next page.
> 2 - The latency to get the next page is far lower than the program 
>     time execution before it will need of the next page.
> 3 - The page is still in memory when the program will 
>     need it.

With good algorithms, the kernel can make some quite proper
decisions on which readahead can be done and which readahead
is too expensive...

I believe Ingo's readahead code (not yet released) does something
like this. It analizes the programs' usage pattern and swaps in
until the page that has 50% probability of usage. If the program
soft-faults one of the preread pages, the kernel reads in the next
one(s) and this goes on until the kernel frees one of the preread
pages.

Rik.
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| Linux memory management tour guide.        H.H.vanRiel@phys.uu.nl |
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