m68k/mm: Port OOM changes to do_page_fault()

Commit d065bd810b6deb67d4897a14bfe21f8eb526ba99
(mm: retry page fault when blocking on disk transfer) and
commit 37b23e0525d393d48a7d59f870b3bc061a30ccdb
(x86,mm: make pagefault killable)

The above commits introduced changes into the x86 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.

Port these changes to m68k.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 34 insertions, 8 deletions

diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index 6b020a8461e7..aeebbb7b30f0 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -72,7 +72,8 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 {
         struct mm_struct *mm = current->mm;
         struct vm_area_struct * vma;
-        int write, fault;
+        int fault;
+        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
 #ifdef DEBUG
         printk ("do page fault:\nregs->sr=%#x, regs->pc=%#lx, address=%#lx, %ld, %p\n",
@@ -87,6 +88,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
         if (in_atomic() || !mm)
                 goto no_context;
 
+retry:
         down_read(&mm->mmap_sem);
 
         vma = find_vma(mm, address);
@@ -117,14 +119,13 @@ good_area:
 #ifdef DEBUG
         printk("do_page_fault: good_area\n");
 #endif
-        write = 0;
         switch (error_code & 3) {
                 default:        /* 3: write, present */
                         /* fall through */
                 case 2:         /* write, not present */
                         if (!(vma->vm_flags & VM_WRITE))
                                 goto acc_err;
-                        write++;
+                        flags |= FAULT_FLAG_WRITE;
                         break;
                 case 1:         /* read, present */
                         goto acc_err;
@@ -139,10 +140,14 @@ good_area:
          * the fault.
          */
 
-        fault = handle_mm_fault(mm, vma, address, write ? FAULT_FLAG_WRITE : 0);
+        fault = handle_mm_fault(mm, vma, address, flags);
 #ifdef DEBUG
         printk("handle_mm_fault returns %d\n",fault);
 #endif
+
+        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+                return 0;
+
         if (unlikely(fault & VM_FAULT_ERROR)) {
                 if (fault & VM_FAULT_OOM)
                         goto out_of_memory;
@@ -150,10 +155,31 @@ good_area:
                         goto bus_err;
                 BUG();
         }
-        if (fault & VM_FAULT_MAJOR)
-                current->maj_flt++;
-        else
-                current->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;
+
+                        /*
+                         * 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 0;