ftrace: convert single large buffer into single pages.

Allocating large buffers for the tracer may fail easily.
This patch converts the buffer from a large ordered allocation
to single pages. It uses the struct page LRU field to link the
pages together.

Later patches may also implement dynamic increasing and decreasing
of the trace buffers.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/trace/trace.h

@@ -54,9 +54,11 @@ struct trace_entry {
  */
 struct trace_array_cpu {
 	void			*trace;
+	void			*trace_current;
+	unsigned		trace_current_idx;
+	struct list_head	trace_pages;
 	unsigned long		trace_idx;
 	atomic_t		disabled;
-	atomic_t		underrun;
 	unsigned long		saved_latency;
 	unsigned long		critical_start;
 	unsigned long		critical_end;
@@ -112,8 +114,10 @@ struct trace_iterator {
 	unsigned long		iter_flags;
 	loff_t			pos;
 	unsigned long		next_idx[NR_CPUS];
+	struct list_head	*next_page[NR_CPUS];
+	unsigned		next_page_idx[NR_CPUS];
+	long			idx;
 	int			cpu;
-	int			idx;
 };
 
 void notrace tracing_reset(struct trace_array_cpu *data);