From 45961722f8e30ceab9d135b1ddc0947d53aef7c3 Mon Sep 17 00:00:00 2001
From: Konstantin Weitz <konstantin.weitz@gmail.com>
Date: Wed, 17 Apr 2013 13:59:32 +0200
Subject: [PATCH] mm: add support for discard of unused ptes

In a virtualized environment and given an appropriate interface the guest
can mark pages as unused while they are free (for the s390 implementation
see git commit 45e576b1c3d00206 "guest page hinting light"). For the host
the unused state is a property of the pte.

This patch adds the primitive 'pte_unused' and code to the host swap out
handler so that pages marked as unused by all mappers are not swapped out
but discarded instead, thus saving one IO for swap out and potentially
another one for swap in.

[ Martin Schwidefsky: patch reordering and simplification ]

Signed-off-by: Konstantin Weitz <konstantin.weitz@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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