writeback: make writeback_control.nr_to_write straight

Pass struct wb_writeback_work all the way down to writeback_sb_inodes(),
and initialize the struct writeback_control there.

struct writeback_control is basically designed to control writeback of a
single file, but we keep abuse it for writing multiple files in
writeback_sb_inodes() and its callers.

It immediately clean things up, e.g. suddenly wbc.nr_to_write vs
work->nr_pages starts to make sense, and instead of saving and restoring
pages_skipped in writeback_sb_inodes it can always start with a clean
zero value.

It also makes a neat IO pattern change: large dirty files are now
written in the full 4MB writeback chunk size, rather than whatever
remained quota in wbc->nr_to_write.

Acked-by: Jan Kara <jack@suse.cz>
Proposed-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 28 insertions, 11 deletions

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 205d14919ef2..3e7662a0cfa3 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -62,6 +62,9 @@ DEFINE_EVENT(writeback_work_class, name, \
 DEFINE_WRITEBACK_WORK_EVENT(writeback_nothread);
 DEFINE_WRITEBACK_WORK_EVENT(writeback_queue);
 DEFINE_WRITEBACK_WORK_EVENT(writeback_exec);
+DEFINE_WRITEBACK_WORK_EVENT(writeback_start);
+DEFINE_WRITEBACK_WORK_EVENT(writeback_written);
+DEFINE_WRITEBACK_WORK_EVENT(writeback_wait);
 
 TRACE_EVENT(writeback_pages_written,
         TP_PROTO(long pages_written),
@@ -101,6 +104,30 @@ DEFINE_WRITEBACK_EVENT(writeback_bdi_register);
 DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);
 DEFINE_WRITEBACK_EVENT(writeback_thread_start);
 DEFINE_WRITEBACK_EVENT(writeback_thread_stop);
+DEFINE_WRITEBACK_EVENT(balance_dirty_start);
+DEFINE_WRITEBACK_EVENT(balance_dirty_wait);
+
+TRACE_EVENT(balance_dirty_written,
+
+        TP_PROTO(struct backing_dev_info *bdi, int written),
+
+        TP_ARGS(bdi, written),
+
+        TP_STRUCT__entry(
+                __array(char,   name, 32)
+                __field(int,    written)
+        ),
+
+        TP_fast_assign(
+                strncpy(__entry->name, dev_name(bdi->dev), 32);
+                __entry->written = written;
+        ),
+
+        TP_printk("bdi %s written %d",
+                  __entry->name,
+                  __entry->written
+        )
+);
 
 DECLARE_EVENT_CLASS(wbc_class,
         TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi),
@@ -114,7 +141,6 @@ DECLARE_EVENT_CLASS(wbc_class,
                 __field(int, for_background)
                 __field(int, for_reclaim)
                 __field(int, range_cyclic)
-                __field(unsigned long, older_than_this)
                 __field(long, range_start)
                 __field(long, range_end)
         ),
@@ -128,14 +154,12 @@ DECLARE_EVENT_CLASS(wbc_class,
                 __entry->for_background = wbc->for_background;
                 __entry->for_reclaim    = wbc->for_reclaim;
                 __entry->range_cyclic   = wbc->range_cyclic;
-                __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("bdi %s: towrt=%ld skip=%ld mode=%d kupd=%d "
-                "bgrd=%d reclm=%d cyclic=%d older=0x%lx "
+                "bgrd=%d reclm=%d cyclic=%d "
                 "start=0x%lx end=0x%lx",
                 __entry->name,
                 __entry->nr_to_write,
@@ -145,7 +169,6 @@ DECLARE_EVENT_CLASS(wbc_class,
                 __entry->for_background,
                 __entry->for_reclaim,
                 __entry->range_cyclic,
-                __entry->older_than_this,
                 __entry->range_start,
                 __entry->range_end)
 )
@@ -154,12 +177,6 @@ DECLARE_EVENT_CLASS(wbc_class,
 DEFINE_EVENT(wbc_class, name, \
         TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi), \
         TP_ARGS(wbc, bdi))
-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);
 DEFINE_WBC_EVENT(wbc_writepage);
 
 TRACE_EVENT(writeback_queue_io,