mm/memory.c: Update local TLB if PTE entry exists

If two threads concurrently fault at the same page, the thread that
won the race updates the PTE and its local TLB. For now, the other
thread gives up, simply does nothing, and continues.

It could happen that this second thread triggers another fault, whereby
it only updates its local TLB while handling the fault. Instead of
triggering another fault, let's directly update the local TLB of the
second thread. Function update_mmu_tlb is used here to update local
TLB on the second thread, and it is defined as empty on other arches.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 329b8c8ca703..fa5c73ff8226 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -188,6 +188,23 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
 }
 #endif
 
+
+/*
+ * If two threads concurrently fault at the same page, the thread that
+ * won the race updates the PTE and its local TLB/Cache. The other thread
+ * gives up, simply does nothing, and continues; on architectures where
+ * software can update TLB,  local TLB can be updated here to avoid next page
+ * fault. This function updates TLB only, do nothing with cache or others.
+ * It is the difference with function update_mmu_cache.
+ */
+#ifndef __HAVE_ARCH_UPDATE_MMU_TLB
+static inline void update_mmu_tlb(struct vm_area_struct *vma,
+				unsigned long address, pte_t *ptep)
+{
+}
+#define __HAVE_ARCH_UPDATE_MMU_TLB
+#endif
+
 /*
  * Some architectures may be able to avoid expensive synchronization
  * primitives when modifications are made to PTE's which are already