[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>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index af7eb087dca7..d98ec49570b8 100644
--- 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..
          */