Vladimir Dergachev wrote:

quoted

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- It shrinks the window size in response to "misses"  - if
  userspace requests a page which is *not* inside the previously-requested
  window, the future window size is shrunk by 25%

This one seems wierd.  If I reference a page that could have been in a
larger read-ahead window, shouldn't I make the window *larger* so that
next time, it *will* be in the window?

That's true.  If the application is walking across a file
touching every fifth page, readahead will stabilise at
its minimum window size, which is less than five pages and
we lose bigtime.   I'm not sure how to fix that while retaining
some sanity in the code.

I am curious: which applications do you know of that actually do this ?

None.  Just a test program which I used for testing readahead!

What about growing the window even if there is a miss as long as misses
are sequential and not further than a fixed amount from the window ?

That would work.  If the window size is less than max, and the
miss occurred inside the max, increase the window to a size which
would have caught that page.  Or to the max.

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