Add a trace event to the ->writepage loop in write_cache_pages to give
visibility into how the ->writepage call is changing variables within the
writeback control structure. Of most interest is how wbc->nr_to_write changes
from call to call, especially with filesystems that write multiple pages
in ->writepage.
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
include/trace/events/writeback.h | 1 +
mm/page-writeback.c | 1 +
2 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 72c1a12..5dda40e 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -244,6 +244,7 @@ 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);
+DEFINE_WBC_EVENT(wbc_writepage);
#endif /* _TRACE_WRITEBACK_H */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 68eb727..caaf954 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -921,6 +921,7 @@ continue_unlock:
if (!clear_page_dirty_for_io(page))
goto continue_unlock;
+ trace_wbc_writepage(wbc);
ret = (*writepage)(page, wbc, data);
if (unlikely(ret)) {
if (ret == AOP_WRITEPAGE_ACTIVATE) {
--
1.7.1
--
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