Re: [RFC] start_aggressive_readahead

[Vladimir Dergachev <volodya@mindspring.com>]

> > > - 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 ?

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 ?

                          Vladimir Dergachev


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