[PATCH] place rmap locking in rmap-locking.h

The rmap locking inlines are causing some header file
dependency/ordering problems - move them out of page-flags.h and into
their own header file.

1 files changed, 33 insertions, 0 deletions

diff --git a/include/linux/rmap-locking.h b/include/linux/rmap-locking.h
new file mode 100644
index 000000000000..302a58f54ca3
--- /dev/null
+++ b/include/linux/rmap-locking.h
@@ -0,0 +1,33 @@
+/*
+ * include/linux/rmap-locking.h
+ *
+ * Locking primitives for exclusive access to a page's reverse-mapping
+ * pte chain.
+ */
+
+static inline void pte_chain_lock(struct page *page)
+{
+	/*
+	 * Assuming the lock is uncontended, this never enters
+	 * the body of the outer loop. If it is contended, then
+	 * within the inner loop a non-atomic test is used to
+	 * busywait with less bus contention for a good time to
+	 * attempt to acquire the lock bit.
+	 */
+	preempt_disable();
+#ifdef CONFIG_SMP
+	while (test_and_set_bit(PG_chainlock, &page->flags)) {
+		while (test_bit(PG_chainlock, &page->flags))
+			cpu_relax();
+	}
+#endif
+}
+
+static inline void pte_chain_unlock(struct page *page)
+{
+#ifdef CONFIG_SMP
+	smp_mb__before_clear_bit();
+	clear_bit(PG_chainlock, &page->flags);
+#endif
+	preempt_enable();
+}