[IA64] Prefetch mmap_sem in ia64_do_page_fault()

Take a hint from an x86_64 optimization by Arjan van de Ven and use it
for ia64.  See a9ba9a3b3897561d01e04cd21433746df46548c0

Prefetch the mmap_sem, which is critical for the performance of the page fault
handler.

Note: mm may be NULL but I guess that is safe.
See 458f935527372499b714bf4f8e646a68bb0f52e3

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index af7eb08..d98ec49 100644 (file)
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -60,6 +60,9 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
        struct siginfo si;
        unsigned long mask;
 
+       /* mmap_sem is performance critical.... */
+       prefetchw(&mm->mmap_sem);
+
        /*
         * If we're in an interrupt or have no user context, we must not take the fault..
         */