powerpc/mm: Only call store_updates_sp() on stores in do_page_fault()

Function store_updates_sp() checks whether the faulting
instruction is a store updating r1. Therefore we can limit its calls
to store exceptions.

This patch is an improvement of commit a7a9dcd882a67 ("powerpc: Avoid
taking a data miss on every userspace instruction miss")

With the same microbenchmark app, run with 500 as argument, on an
MPC885 we get:

Before this patch: 152000 DTLB misses
After this patch:  147000 DTLB misses

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 3a7d580fdc59df87f716f7b5427ff7e963c336ca..67fefb59d40e52e5b65fa47d5562ac1016d1c6b1 100644 (file)
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -287,7 +287,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
         * can result in fault, which will cause a deadlock when called with
         * mmap_sem held
         */
-       if (!is_exec && user_mode(regs))
+       if (is_write && user_mode(regs))
                store_update_sp = store_updates_sp(regs);
 
        if (user_mode(regs))