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>

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index d11b903c2edb8aa6cf4b40f73a5428d7986919d7..32095928365ce10d08b3ece1f22e66eca0613e67 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -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);

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index a261e86e61facf89041f0fdf5bff30ee593ae692..3213b90237944373d603ea9108fd8494a558182f 100644 (file)
--- 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;

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 8b325aa525eb5d314b893ed97c8231e59e375233..149f8b81590403a702555a323e4cfb8d7d6a55cd 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -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 @@ free_running:
                 */
                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 @@ free_running:
 
 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,