Commit f1ab2831 authored by Tang Yizhou's avatar Tang Yizhou Committed by Andrew Morton
Browse files

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: default avatarTang 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 70478a55

include/linux/writeback.h

+23 −0
Original line number Diff line number Diff line
@@ -313,6 +313,29 @@ static inline void cgroup_writeback_umount(struct super_block *sb) 
/*

 * mm/page-writeback.c

 */

/* consolidated parameters for balance_dirty_pages() and its subroutines */

struct dirty_throttle_control {

#ifdef CONFIG_CGROUP_WRITEBACK

	struct wb_domain	*dom;

	struct dirty_throttle_control *gdtc;	/* only set in memcg dtc's */

#endif

	struct bdi_writeback	*wb;

	struct fprop_local_percpu *wb_completions;



	unsigned long		avail;		/* dirtyable */

	unsigned long		dirty;		/* file_dirty + write + nfs */

	unsigned long		thresh;		/* dirty threshold */

	unsigned long		bg_thresh;	/* dirty background threshold */



	unsigned long		wb_dirty;	/* per-wb counterparts */

	unsigned long		wb_thresh;

	unsigned long		wb_bg_thresh;



	unsigned long		pos_ratio;

	bool			freerun;

	bool			dirty_exceeded;

};



void laptop_io_completion(struct backing_dev_info *info);

void laptop_sync_completion(void);

void laptop_mode_timer_fn(struct timer_list *t);

include/trace/events/writeback.h

+6 −10
Original line number Diff line number Diff line
@@ -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;

mm/page-writeback.c

+2 −33
Original line number Diff line number Diff line
@@ -120,29 +120,6 @@ EXPORT_SYMBOL(laptop_mode); 


struct wb_domain global_wb_domain;



/* consolidated parameters for balance_dirty_pages() and its subroutines */

struct dirty_throttle_control {

#ifdef CONFIG_CGROUP_WRITEBACK

	struct wb_domain	*dom;

	struct dirty_throttle_control *gdtc;	/* only set in memcg dtc's */

#endif

	struct bdi_writeback	*wb;

	struct fprop_local_percpu *wb_completions;



	unsigned long		avail;		/* dirtyable */

	unsigned long		dirty;		/* file_dirty + write + nfs */

	unsigned long		thresh;		/* dirty threshold */

	unsigned long		bg_thresh;	/* dirty background threshold */



	unsigned long		wb_dirty;	/* per-wb counterparts */

	unsigned long		wb_thresh;

	unsigned long		wb_bg_thresh;



	unsigned long		pos_ratio;

	bool			freerun;

	bool			dirty_exceeded;

};



/*

 * Length of period for aging writeout fractions of bdis. This is an

 * arbitrarily chosen number. The longer the period, the slower fractions will
@@ -1962,11 +1939,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb, 
		 */

		if (pause < min_pause) {

			trace_balance_dirty_pages(wb,

						  sdtc->thresh,

						  sdtc->bg_thresh,

						  sdtc->dirty,

						  sdtc->wb_thresh,

						  sdtc->wb_dirty,

						  sdtc,

						  dirty_ratelimit,

						  task_ratelimit,

						  pages_dirtied,
@@ -1991,11 +1964,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb, 


pause:

		trace_balance_dirty_pages(wb,

					  sdtc->thresh,

					  sdtc->bg_thresh,

					  sdtc->dirty,

					  sdtc->wb_thresh,

					  sdtc->wb_dirty,

					  sdtc,

					  dirty_ratelimit,

					  task_ratelimit,

					  pages_dirtied,