sh: lockless UTLB miss fast-path.

With the refactored update_mmu_cache() introduced in older kernels,
there's no longer any need to take the page_table_lock in this path,
so simply drop it completely.

Without this, performance degradation is seen on SMP on heavily
threaded workloads that don't use the split ptlock, and ultimately
we have no reason to contend for the lock in the first place.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index c56a5fabcd0f9678c01282a384a83ad96dca2c3d..60d74f793a1d33969a68d6c303b37dda4f4cd214 100644 (file)
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -258,9 +258,6 @@ asmlinkage int __kprobes __do_page_fault(struct pt_regs *regs,
        pmd_t *pmd;
        pte_t *pte;
        pte_t entry;
-       struct mm_struct *mm = current->mm;
-       spinlock_t *ptl = NULL;
-       int ret = 1;
 
 #ifdef CONFIG_SH_KGDB
        if (kgdb_nofault && kgdb_bus_err_hook)
@@ -274,12 +271,11 @@ asmlinkage int __kprobes __do_page_fault(struct pt_regs *regs,
         */
        if (address >= P3SEG && address < P3_ADDR_MAX) {
                pgd = pgd_offset_k(address);
-               mm = NULL;
        } else {
-               if (unlikely(address >= TASK_SIZE || !mm))
+               if (unlikely(address >= TASK_SIZE || !current->mm))
                        return 1;
 
-               pgd = pgd_offset(mm, address);
+               pgd = pgd_offset(current->mm, address);
        }
 
        pud = pud_offset(pgd, address);
@@ -289,16 +285,12 @@ asmlinkage int __kprobes __do_page_fault(struct pt_regs *regs,
        if (pmd_none_or_clear_bad(pmd))
                return 1;
 
-       if (mm)
-               pte = pte_offset_map_lock(mm, pmd, address, &ptl);
-       else
-               pte = pte_offset_kernel(pmd, address);
-
+       pte = pte_offset_kernel(pmd, address);
        entry = *pte;
        if (unlikely(pte_none(entry) || pte_not_present(entry)))
-               goto unlock;
+               return 1;
        if (unlikely(writeaccess && !pte_write(entry)))
-               goto unlock;
+               return 1;
 
        if (writeaccess)
                entry = pte_mkdirty(entry);
@@ -306,9 +298,6 @@ asmlinkage int __kprobes __do_page_fault(struct pt_regs *regs,
 
        set_pte(pte, entry);
        update_mmu_cache(NULL, address, entry);
-       ret = 0;
-unlock:
-       if (mm)
-               pte_unmap_unlock(pte, ptl);
-       return ret;
+
+       return 0;
 }