Page table optimizations in Linux and FreeBSD

[David S. Miller]

   Date:   Thu, 20 Jan 2000 19:21:27 +0100
   From: Jamie Lokier <lkd en tantalophile.demon.co.uk>

   The do mention pre-faulting and pre-emptive page out.  I don't know if
   we do pre-faulting but I believe we do pre-emptive page out now.

We experimented with pre-faulting.  It's a win early on system bootup
for things like libc, but after some time most of libc is in core
and pre-faulting becomes a lose.

Last time I checked out the FreeBSD implementation of pre-faulting
they have a limit to the number of pages they'll prefault for a given
mapped vnode.  They selected the "most likely to be beneficial" pages,
and you can do this with fault counting etc. but as your job mixture
becomes more varied on the system these page selection choice begin
to be arbitrary.

Later,
David S. Miller
davem en redhat.com

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