x86,pat: Reduce contention on the memtype_lock -V4

Tracking memtype on x86 uses a single global spin_lock for either reading
or changing the memory type.  This includes changes made to page flags
which is perfectly parallel.

Part one of the patchset makes the page-based tracking use cmpxchg
without a need for a lock.

Part two of the patchset converts the spin_lock into a read/write lock.


To: Ingo Molnar <mingo@redhat.com>
To: H. Peter Anvin <hpa@zytor.com>
To: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Robin Holt <holt@sgi.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@gmail.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org
Cc: Rafael Wysocki <rjw@novell.com>

---

 arch/x86/include/asm/cacheflush.h |   44 +++++++++++++++++++++-----------------
 arch/x86/mm/pat.c                 |   30 +++++++++----------------
 2 files changed, 36 insertions(+), 38 deletions(-)

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