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Subject[PATCH 2/4] writeback: Add tracing to balance_dirty_pages
Date
From: Dave Chinner <dchinner@redhat.com>

Tracing high level background writeback events is good, but it doesn't
give the entire picture. Add IO dispatched by foreground throttling to the
writeback events.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/fs-writeback.c | 5 ++
include/trace/events/writeback.h | 77 ++++++++++++++++++++++++++++++++++++++
mm/page-writeback.c | 4 ++
3 files changed, 86 insertions(+), 0 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 3f5f0a5..5214b61 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -752,7 +752,11 @@ static long wb_writeback(struct bdi_writeback *wb,
wbc.more_io = 0;
wbc.nr_to_write = MAX_WRITEBACK_PAGES;
wbc.pages_skipped = 0;
+
+ trace_wbc_writeback_start(&wbc);
writeback_inodes_wb(wb, &wbc);
+ trace_wbc_writeback_written(&wbc);
+
args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;

@@ -780,6 +784,7 @@ static long wb_writeback(struct bdi_writeback *wb,
if (!list_empty(&wb->b_more_io)) {
inode = list_entry(wb->b_more_io.prev,
struct inode, i_list);
+ trace_wbc_writeback_wait(&wbc);
inode_wait_for_writeback(inode);
}
spin_unlock(&inode_lock);
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index df76457..02f34a5 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -165,6 +165,83 @@ TRACE_EVENT(writeback_bdi_register,
TP_printk("%s: %s", __entry->name,
__entry->start ? "registered" : "unregistered")
);
+
+/* pass flags explicitly */
+DECLARE_EVENT_CLASS(wbc_class,
+ TP_PROTO(struct writeback_control *wbc),
+ TP_ARGS(wbc),
+ TP_STRUCT__entry(
+ __field(unsigned int, wbc)
+ __array(char, name, 16)
+ __field(long, nr_to_write)
+ __field(long, pages_skipped)
+ __field(int, sb)
+ __field(int, sync_mode)
+ __field(int, nonblocking)
+ __field(int, encountered_congestion)
+ __field(int, for_kupdate)
+ __field(int, for_background)
+ __field(int, for_reclaim)
+ __field(int, range_cyclic)
+ __field(int, more_io)
+ __field(unsigned long, older_than_this)
+ __field(long, range_start)
+ __field(long, range_end)
+ ),
+
+ TP_fast_assign(
+ char *__name = "(none)";
+
+ __entry->wbc = (unsigned long)wbc & 0xffff;
+ if (wbc->bdi)
+ strncpy(__entry->name, dev_name(wbc->bdi->dev), 16);
+ else
+ strncpy(__entry->name, __name, 16);
+ __entry->nr_to_write = wbc->nr_to_write;
+ __entry->pages_skipped = wbc->pages_skipped;
+ __entry->sb = !!wbc->sb;
+ __entry->sync_mode = wbc->sync_mode;
+ __entry->for_kupdate = wbc->for_kupdate;
+ __entry->for_background = wbc->for_background;
+ __entry->for_reclaim = wbc->for_reclaim;
+ __entry->range_cyclic = wbc->range_cyclic;
+ __entry->more_io = wbc->more_io;
+ __entry->older_than_this = wbc->older_than_this ?
+ *wbc->older_than_this : 0;
+ __entry->range_start = (long)wbc->range_start;
+ __entry->range_end = (long)wbc->range_end;
+ ),
+
+ TP_printk("dev %s wbc=%x towrt=%ld skip=%ld sb=%d mode=%d kupd=%d "
+ "bgrd=%d reclm=%d cyclic=%d more=%d older=0x%lx "
+ "start=0x%lx end=0x%lx",
+ __entry->name,
+ __entry->wbc,
+ __entry->nr_to_write,
+ __entry->pages_skipped,
+ __entry->sb,
+ __entry->sync_mode,
+ __entry->for_kupdate,
+ __entry->for_background,
+ __entry->for_reclaim,
+ __entry->range_cyclic,
+ __entry->more_io,
+ __entry->older_than_this,
+ __entry->range_start,
+ __entry->range_end)
+)
+
+#define DEFINE_WBC_EVENT(name) \
+DEFINE_EVENT(wbc_class, name, \
+ TP_PROTO(struct writeback_control *wbc), \
+ TP_ARGS(wbc))
+DEFINE_WBC_EVENT(wbc_writeback_start);
+DEFINE_WBC_EVENT(wbc_writeback_written);
+DEFINE_WBC_EVENT(wbc_writeback_wait);
+DEFINE_WBC_EVENT(wbc_balance_dirty_start);
+DEFINE_WBC_EVENT(wbc_balance_dirty_written);
+DEFINE_WBC_EVENT(wbc_balance_dirty_wait);
+
#endif /* _TRACE_WRITEBACK_H */

/* This part must be outside protection */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0b19943..d45f59e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -34,6 +34,7 @@
#include <linux/syscalls.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
+#include <trace/events/writeback.h>

/*
* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
@@ -536,11 +537,13 @@ static void balance_dirty_pages(struct address_space *mapping,
* threshold otherwise wait until the disk writes catch
* up.
*/
+ trace_wbc_balance_dirty_start(&wbc);
if (bdi_nr_reclaimable > bdi_thresh) {
writeback_inodes_wbc(&wbc);
pages_written += write_chunk - wbc.nr_to_write;
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
+ trace_wbc_balance_dirty_written(&wbc);
}

/*
@@ -566,6 +569,7 @@ static void balance_dirty_pages(struct address_space *mapping,
if (pages_written >= write_chunk)
break; /* We've done our duty */

+ trace_wbc_balance_dirty_wait(&wbc);
__set_current_state(TASK_INTERRUPTIBLE);
io_schedule_timeout(pause);

--
1.6.5


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