writeback: let trace_balance_dirty_pages() take struct dtc as parameter

Patch series "Fix calculations in trace_balance_dirty_pages() for cgwb", v2.

In my experiment, I found that the output of trace_balance_dirty_pages()
in the cgroup writeback scenario was strange because
trace_balance_dirty_pages() always uses global_wb_domain.dirty_limit for
related calculations instead of the dirty_limit of the corresponding
memcg's wb_domain.

The basic idea of the fix is to store the hard dirty limit value computed
in wb_position_ratio() into struct dirty_throttle_control and use it for
calculations in trace_balance_dirty_pages().


This patch (of 3):

Currently, trace_balance_dirty_pages() already has 12 parameters.  In the
patch #3, I initially attempted to introduce an additional parameter. 
However, in include/linux/trace_events.h, bpf_trace_run12() only supports
up to 12 parameters and bpf_trace_run13() does not exist.

To reduce the number of parameters in trace_balance_dirty_pages(), we can
make it accept a pointer to struct dirty_throttle_control as a parameter. 
To achieve this, we need to move the definition of struct
dirty_throttle_control from mm/page-writeback.c to
include/linux/writeback.h.

Link: https://lkml.kernel.org/r/20250304110318.159567-1-yizhou.tang@shopee.com
Link: https://lkml.kernel.org/r/20250304110318.159567-2-yizhou.tang@shopee.com
Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Tang Yizhou <yizhou.tang@shopee.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 6 insertions, 10 deletions

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index a261e86e61fa..3213b9023794 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -629,11 +629,7 @@ TRACE_EVENT(bdi_dirty_ratelimit,
 TRACE_EVENT(balance_dirty_pages,
 
 	TP_PROTO(struct bdi_writeback *wb,
-		 unsigned long thresh,
-		 unsigned long bg_thresh,
-		 unsigned long dirty,
-		 unsigned long bdi_thresh,
-		 unsigned long bdi_dirty,
+		 struct dirty_throttle_control *dtc,
 		 unsigned long dirty_ratelimit,
 		 unsigned long task_ratelimit,
 		 unsigned long dirtied,
@@ -641,7 +637,7 @@ TRACE_EVENT(balance_dirty_pages,
 		 long pause,
 		 unsigned long start_time),
 
-	TP_ARGS(wb, thresh, bg_thresh, dirty, bdi_thresh, bdi_dirty,
+	TP_ARGS(wb, dtc,
 		dirty_ratelimit, task_ratelimit,
 		dirtied, period, pause, start_time),
 
@@ -664,16 +660,16 @@ TRACE_EVENT(balance_dirty_pages,
 	),
 
 	TP_fast_assign(
-		unsigned long freerun = (thresh + bg_thresh) / 2;
+		unsigned long freerun = (dtc->thresh + dtc->bg_thresh) / 2;
 		strscpy_pad(__entry->bdi, bdi_dev_name(wb->bdi), 32);
 
 		__entry->limit		= global_wb_domain.dirty_limit;
 		__entry->setpoint	= (global_wb_domain.dirty_limit +
 						freerun) / 2;
-		__entry->dirty		= dirty;
+		__entry->dirty		= dtc->dirty;
 		__entry->bdi_setpoint	= __entry->setpoint *
-						bdi_thresh / (thresh + 1);
-		__entry->bdi_dirty	= bdi_dirty;
+						dtc->wb_thresh / (dtc->thresh + 1);
+		__entry->bdi_dirty	= dtc->wb_dirty;
 		__entry->dirty_ratelimit = KBps(dirty_ratelimit);
 		__entry->task_ratelimit	= KBps(task_ratelimit);
 		__entry->dirtied	= dirtied;