[patch 09/17] LTTng instrumentation - filemap

[Mathieu Desnoyers]

Instrumentation of waits caused by memory accesses on mmap regions.

Those tracepoints are used by LTTng.

About the performance impact of tracepoints (which is comparable to markers),
even without immediate values optimizations, tests done by Hideo Aoki on ia64
show no regression. His test case was using hackbench on a kernel where
scheduler instrumentation (about 5 events in code scheduler code) was added.
See the "Tracepoints" patch header for performance result detail.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: linux-mm@xxxxxxxxx
CC: Dave Hansen <haveblue@xxxxxxxxxx>
CC: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
CC: 'Peter Zijlstra' <peterz@xxxxxxxxxxxxx>
CC: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
CC: 'Ingo Molnar' <mingo@xxxxxxx>
CC: 'Hideo AOKI' <haoki@xxxxxxxxxx>
CC: Takashi Nishiie <t-nishiie@xxxxxxxxxxxxxxxxxx>
CC: 'Steven Rostedt' <rostedt@xxxxxxxxxxx>
CC: Eduard - Gabriel Munteanu <eduard.munteanu@xxxxxxxxxxx>
---
 include/trace/filemap.h |   13 +++++++++++++
 mm/filemap.c            |    3 +++
 2 files changed, 16 insertions(+)

Index: linux-2.6-lttng/mm/filemap.c
===================================================================
--- linux-2.6-lttng.orig/mm/filemap.c	2008-07-15 14:51:50.000000000 -0400
+++ linux-2.6-lttng/mm/filemap.c	2008-07-15 15:14:46.000000000 -0400
@@ -33,6 +33,7 @@
 #include <linux/cpuset.h>
 #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
 #include <linux/memcontrol.h>
+#include <trace/filemap.h>
 #include "internal.h"
 
 /*
@@ -541,9 +542,11 @@ void wait_on_page_bit(struct page *page,
 {
 	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
 
+	trace_filemap_wait_start(page, bit_nr);
 	if (test_bit(bit_nr, &page->flags))
 		__wait_on_bit(page_waitqueue(page), &wait, sync_page,
 							TASK_UNINTERRUPTIBLE);
+	trace_filemap_wait_end(page, bit_nr);
 }
 EXPORT_SYMBOL(wait_on_page_bit);
 
Index: linux-2.6-lttng/include/trace/filemap.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/trace/filemap.h	2008-07-15 15:14:46.000000000 -0400
@@ -0,0 +1,13 @@
+#ifndef _TRACE_FILEMAP_H
+#define _TRACE_FILEMAP_H
+
+#include <linux/tracepoint.h>
+
+DEFINE_TRACE(filemap_wait_start,
+	TPPROTO(struct page *page, int bit_nr),
+	TPARGS(page, bit_nr));
+DEFINE_TRACE(filemap_wait_end,
+	TPPROTO(struct page *page, int bit_nr),
+	TPARGS(page, bit_nr));
+
+#endif

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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