Re: Anticipatory prefaulting in the page fault handler V2

From: Andi Kleen
Date: Thu Dec 16 2004 - 02:29:26 EST

Christoph Lameter <clameter@xxxxxxx> writes:
> If a fault occurred for page x and is then followed by page x+1 then it may
> be reasonable to expect another page fault at x+2 in the future. If page
> table entries for x+1 and x+2 would be prepared in the fault handling for
> page x+1 then the overhead of taking a fault for x+2 is avoided. However
> page x+2 may never be used and thus we may have increased the rss
> of an application unnecessarily. The swapper will take care of removing
> that page if memory should get tight.

I would be very careful with this. Windows does something like this
by default and one application that I know needs twice as much swap+memory
on Windows than on Linux because of this. Since it uses a lot of memory
it would be a bad regression.

When you add it there should be at least some easy way for an application
to turn it off (madvise and probably sysctl?) and make the heuristic very

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