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>

1 files changed, 32 insertions, 5 deletions

diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index d194c0427b26..0d231adfe576 100644
--- 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;