[S390] mm: add page fault retry handling

s390 arch backend for d065bd81 "mm: retry page fault when blocking on
disk transfer".

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

1 files changed, 28 insertions, 13 deletions

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index b57723aee848..fe103e891e7a 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -280,7 +280,8 @@ static inline int do_exception(struct pt_regs *regs, int access,
         struct mm_struct *mm;
         struct vm_area_struct *vma;
         unsigned long address;
-        int fault, write;
+        unsigned int flags;
+        int fault;
 
         if (notify_page_fault(regs))
                 return 0;
@@ -299,6 +300,10 @@ static inline int do_exception(struct pt_regs *regs, int access,
 
         address = trans_exc_code & __FAIL_ADDR_MASK;
         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);
+        flags = FAULT_FLAG_ALLOW_RETRY;
+        if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
+                flags |= FAULT_FLAG_WRITE;
+retry:
         down_read(&mm->mmap_sem);
 
         fault = VM_FAULT_BADMAP;
@@ -328,21 +333,31 @@ static inline int do_exception(struct pt_regs *regs, int access,
          * make sure we exit gracefully rather than endlessly redo
          * the fault.
          */
-        write = (access == VM_WRITE ||
-                 (trans_exc_code & store_indication) == 0x400) ?
-                FAULT_FLAG_WRITE : 0;
-        fault = handle_mm_fault(mm, vma, address, write);
+        fault = handle_mm_fault(mm, vma, address, flags);
         if (unlikely(fault & VM_FAULT_ERROR))
                 goto out_up;
 
-        if (fault & VM_FAULT_MAJOR) {
-                tsk->maj_flt++;
-                perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
-                                     regs, address);
-        } else {
-                tsk->min_flt++;
-                perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
-                                     regs, address);
+        /*
+         * 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) {
+                        tsk->maj_flt++;
+                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
+                                      regs, address);
+                } else {
+                        tsk->min_flt++;
+                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
+                                      regs, address);
+                }
+                if (fault & VM_FAULT_RETRY) {
+                        /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
+                         * of starvation. */
+                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
+                        goto retry;
+                }
         }
         /*
          * The instruction that caused the program check will