nios2: Port OOM changes to do_page_fault()

Commit d065bd810b6d ("mm: retry page fault when blocking on disk transfer") and
and commit 37b23e0525d3 ("x86,mm: make pagefault killable")

The above commits introduced changes into the nios2 pagefault handler
for making the page fault handler retryable as well as killable.

These changes reduce the mmap_sem hold time, which is crucial
during OOM killer invocation.

Signed-off-by: Ley Foon Tan <lftan@altera.com>

diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index d194c04..0d231ad 100644 (file)
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -47,7 +47,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
        struct mm_struct *mm = tsk->mm;
        int code = SEGV_MAPERR;
        int fault;
-       unsigned int flags = 0;
+       unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
        cause >>= 2;
 
@@ -86,6 +86,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
        if (!down_read_trylock(&mm->mmap_sem)) {
                if (!user_mode(regs) && !search_exception_tables(regs->ea))
                        goto bad_area_nosemaphore;
+retry:
                down_read(&mm->mmap_sem);
        }
 
@@ -132,6 +133,10 @@ survive:
         * the fault.
         */
        fault = handle_mm_fault(mm, vma, address, flags);
+
+       if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+               return;
+
        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM)
                        goto out_of_memory;
@@ -141,10 +146,32 @@ survive:
                        goto do_sigbus;
                BUG();
        }
-       if (fault & VM_FAULT_MAJOR)
-               tsk->maj_flt++;
-       else
-               tsk->min_flt++;
+
+       /*
+        * Major/minor page fault accounting is only done on the
+        * initial attempt. If we go through a retry, it is extremely
+        * likely that the page will be found in page cache at that point.
+        */
+       if (flags & FAULT_FLAG_ALLOW_RETRY) {
+               if (fault & VM_FAULT_MAJOR)
+                       current->maj_flt++;
+               else
+                       current->min_flt++;
+               if (fault & VM_FAULT_RETRY) {
+                       /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
+                        * of starvation. */
+                       flags &= ~FAULT_FLAG_ALLOW_RETRY;
+                       flags |= FAULT_FLAG_TRIED;
+
+                       /*
+                        * No need to up_read(&mm->mmap_sem) as we would
+                        * have already released it in __lock_page_or_retry
+                        * in mm/filemap.c.
+                        */
+
+                       goto retry;
+               }
+       }
 
        up_read(&mm->mmap_sem);
        return;