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Subject[PATCH 1/4] writeback: initial tracing support
Date
From: From: Jens Axboe <jens.axboe@oracle.com>

Trace queue/sched/exec parts of the writeback loop.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/fs-writeback.c | 51 +++++-------
include/linux/writeback.h | 27 ++++++
include/trace/events/writeback.h | 171 ++++++++++++++++++++++++++++++++++++++
mm/backing-dev.c | 5 +
4 files changed, 224 insertions(+), 30 deletions(-)
create mode 100644 include/trace/events/writeback.h
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 76fc4d5..3f5f0a5 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -25,7 +25,9 @@
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/buffer_head.h>
+#include <linux/ftrace.h>
#include "internal.h"
+#include <trace/events/writeback.h>

#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)

@@ -34,33 +36,6 @@
*/
int nr_pdflush_threads;

-/*
- * Passed into wb_writeback(), essentially a subset of writeback_control
- */
-struct wb_writeback_args {
- long nr_pages;
- struct super_block *sb;
- enum writeback_sync_modes sync_mode;
- int for_kupdate:1;
- int range_cyclic:1;
- int for_background:1;
-};
-
-/*
- * Work items for the bdi_writeback threads
- */
-struct bdi_work {
- struct list_head list; /* pending work list */
- struct rcu_head rcu_head; /* for RCU free/clear of work */
-
- unsigned long seen; /* threads that have seen this work */
- atomic_t pending; /* number of threads still to do work */
-
- struct wb_writeback_args args; /* writeback arguments */
-
- unsigned long state; /* flag bits, see WS_* */
-};
-
enum {
WS_USED_B = 0,
WS_ONSTACK_B,
@@ -135,6 +110,8 @@ static void wb_work_complete(struct bdi_work *work)

static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
{
+ trace_writeback_clear(work);
+
/*
* The caller has retrieved the work arguments from this work,
* drop our reference. If this is the last ref, delete and free it
@@ -170,12 +147,16 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
* If the default thread isn't there, make sure we add it. When
* it gets created and wakes up, we'll run this work.
*/
- if (unlikely(list_empty_careful(&bdi->wb_list)))
+ if (unlikely(list_empty_careful(&bdi->wb_list))) {
+ trace_writeback_sched(bdi, work, "default");
wake_up_process(default_backing_dev_info.wb.task);
- else {
+ } else {
struct bdi_writeback *wb = &bdi->wb;
+ struct task_struct *task = wb->task;

- if (wb->task)
+ trace_writeback_sched(bdi, work, task ? "task" : "notask");
+
+ if (task)
wake_up_process(wb->task);
}
}
@@ -202,6 +183,7 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
work = kmalloc(sizeof(*work), GFP_ATOMIC);
if (work) {
bdi_work_init(work, args);
+ trace_writeback_queue(bdi, args);
bdi_queue_work(bdi, work);
} else {
struct bdi_writeback *wb = &bdi->wb;
@@ -235,6 +217,7 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
bdi_work_init(&work, &args);
work.state |= WS_ONSTACK;

+ trace_writeback_queue(bdi, &args);
bdi_queue_work(bdi, &work);
bdi_wait_on_work_clear(&work);
}
@@ -880,6 +863,8 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
if (force_wait)
work->args.sync_mode = args.sync_mode = WB_SYNC_ALL;

+ trace_writeback_exec(work);
+
/*
* If this isn't a data integrity operation, just notify
* that we have seen this work and we are now starting it.
@@ -915,9 +900,13 @@ int bdi_writeback_task(struct bdi_writeback *wb)
unsigned long wait_jiffies = -1UL;
long pages_written;

+ trace_writeback_thread_start(1);
+
while (!kthread_should_stop()) {
pages_written = wb_do_writeback(wb, 0);

+ trace_writeback_pages_written(pages_written);
+
if (pages_written)
last_active = jiffies;
else if (wait_jiffies != -1UL) {
@@ -938,6 +927,8 @@ int bdi_writeback_task(struct bdi_writeback *wb)
try_to_freeze();
}

+ trace_writeback_thread_start(0);
+
return 0;
}

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 76e8903..b2d615f 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -22,6 +22,33 @@ enum writeback_sync_modes {
};

/*
+ * Passed into wb_writeback(), essentially a subset of writeback_control
+ */
+struct wb_writeback_args {
+ long nr_pages;
+ struct super_block *sb;
+ enum writeback_sync_modes sync_mode;
+ int for_kupdate:1;
+ int range_cyclic:1;
+ int for_background:1;
+};
+
+/*
+ * Work items for the bdi_writeback threads
+ */
+struct bdi_work {
+ struct list_head list; /* pending work list */
+ struct rcu_head rcu_head; /* for RCU free/clear of work */
+
+ unsigned long seen; /* threads that have seen this work */
+ atomic_t pending; /* number of threads still to do work */
+
+ struct wb_writeback_args args; /* writeback arguments */
+
+ unsigned long state; /* flag bits, see WS_* */
+};
+
+/*
* A control structure which tells the writeback code what to do. These are
* always on the stack, and hence need no locking. They are always initialised
* in a manner such that unspecified fields are set to zero.
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
new file mode 100644
index 0000000..df76457
--- /dev/null
+++ b/include/trace/events/writeback.h
@@ -0,0 +1,171 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM writeback
+
+#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_WRITEBACK_H
+
+#include <linux/backing-dev.h>
+#include <linux/writeback.h>
+
+TRACE_EVENT(writeback_queue,
+
+ TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_args *args),
+
+ TP_ARGS(bdi, args),
+
+ TP_STRUCT__entry(
+ __array(char, name, 16)
+ __field(long, nr_pages)
+ __field(int, sb)
+ __field(int, sync_mode)
+ __field(int, for_kupdate)
+ __field(int, range_cyclic)
+ __field(int, for_background)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, dev_name(bdi->dev), 16);
+ __entry->nr_pages = args->nr_pages;
+ __entry->sb = !!args->sb;
+ __entry->for_kupdate = args->for_kupdate;
+ __entry->range_cyclic = args->range_cyclic;
+ __entry->for_background = args->for_background;
+ ),
+
+ TP_printk("%s: pages=%ld, sb=%d, kupdate=%d, range_cyclic=%d "
+ "for_background=%d", __entry->name, __entry->nr_pages,
+ __entry->sb, __entry->for_kupdate,
+ __entry->range_cyclic, __entry->for_background)
+);
+
+TRACE_EVENT(writeback_sched,
+
+ TP_PROTO(struct backing_dev_info *bdi, struct bdi_work *work,
+ const char *msg),
+
+ TP_ARGS(bdi, work, msg),
+
+ TP_STRUCT__entry(
+ __array(char, name, 16)
+ __field(unsigned int, work)
+ __array(char, task, 8)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, dev_name(bdi->dev), 16);
+ __entry->work = (unsigned long) work & 0xffff;
+ snprintf(__entry->task, 8, "%s", msg);
+ ),
+
+ TP_printk("work=%x, task=%s", __entry->work, __entry->task)
+);
+
+TRACE_EVENT(writeback_exec,
+
+ TP_PROTO(struct bdi_work *work),
+
+ TP_ARGS(work),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, work)
+ __field(long, nr_pages)
+ __field(int, sb)
+ __field(int, sync_mode)
+ __field(int, for_kupdate)
+ __field(int, range_cyclic)
+ __field(int, for_background)
+ ),
+
+ TP_fast_assign(
+ __entry->work = (unsigned long) work & 0xffff;
+ __entry->nr_pages = work->args.nr_pages;
+ __entry->sb = !!work->args.sb;
+ __entry->for_kupdate = work->args.for_kupdate;
+ __entry->range_cyclic = work->args.range_cyclic;
+ __entry->for_background = work->args.for_background;
+
+ ),
+
+ TP_printk("work=%x pages=%ld, sb=%d, kupdate=%d, range_cyclic=%d"
+ " for_background=%d", __entry->work,
+ __entry->nr_pages, __entry->sb, __entry->for_kupdate,
+ __entry->range_cyclic, __entry->for_background)
+);
+
+TRACE_EVENT(writeback_clear,
+
+ TP_PROTO(struct bdi_work *work),
+
+ TP_ARGS(work),
+
+ TP_STRUCT__entry(
+ __field(struct bdi_work *, work)
+ __field(int, refs)
+ ),
+
+ TP_fast_assign(
+ __entry->work = work;
+ __entry->refs = atomic_read(&work->pending);
+ ),
+
+ TP_printk("work=%p, refs=%d", __entry->work, __entry->refs)
+);
+
+TRACE_EVENT(writeback_pages_written,
+
+ TP_PROTO(long pages_written),
+
+ TP_ARGS(pages_written),
+
+ TP_STRUCT__entry(
+ __field(long, pages)
+ ),
+
+ TP_fast_assign(
+ __entry->pages = pages_written;
+ ),
+
+ TP_printk("%ld", __entry->pages)
+);
+
+
+TRACE_EVENT(writeback_thread_start,
+
+ TP_PROTO(int start),
+
+ TP_ARGS(start),
+
+ TP_STRUCT__entry(
+ __field(int, start)
+ ),
+
+ TP_fast_assign(
+ __entry->start = start;
+ ),
+
+ TP_printk("%s", __entry->start ? "started" : "exited")
+);
+
+TRACE_EVENT(writeback_bdi_register,
+
+ TP_PROTO(const char *name, int start),
+
+ TP_ARGS(name, start),
+
+ TP_STRUCT__entry(
+ __array(char, name, 16)
+ __field(int, start)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->name, name, 16);
+ __entry->start = start;
+ ),
+
+ TP_printk("%s: %s", __entry->name,
+ __entry->start ? "registered" : "unregistered")
+);
+#endif /* _TRACE_WRITEBACK_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 0e8ca03..2323e92 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -11,6 +11,9 @@
#include <linux/writeback.h>
#include <linux/device.h>

+#define CREATE_TRACE_POINTS
+#include <trace/events/writeback.h>
+
void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
}
@@ -570,6 +573,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,

bdi_debug_register(bdi, dev_name(dev));
set_bit(BDI_registered, &bdi->state);
+ trace_writeback_bdi_register(dev_name(dev), 1);
exit:
return ret;
}
@@ -632,6 +636,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
void bdi_unregister(struct backing_dev_info *bdi)
{
if (bdi->dev) {
+ trace_writeback_bdi_register(dev_name(bdi->dev), 0);
bdi_prune_sb(bdi);

if (!bdi_cap_flush_forker(bdi))
--
1.6.5


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