perf: Rebase max unprivileged mlock threshold on top of page size

perf: Rebase max unprivileged mlock threshold on top of page size

BugLink: http://bugs.launchpad.net/bugs/761134

commit 20443384fe090c5f8aeb016e7e85659c5bbdd69f upstream.

Ensure we allow 512 kiB + 1 page for user control without
assuming a 4096 bytes page size.

Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <1301535209-9679-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>