[PATCH] ftrace: Add information on number of page groups allocated

[Steven Rostedt (VMware)]

Looking for ways to shrink the size of the dyn_ftrace structure, knowing the
information about how many pages and the number of groups of those pages, is
useful in working out the best ways to save on memory.

This adds one info print on how many groups of pages were used to allocate
the ftrace dyn_ftrace structures, and also shows the number of pages and
groups in the dyn_ftrace_total_info (which is used for debugging).

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/ftrace.c | 14 ++++++++++++++
 kernel/trace/trace.c  | 21 +++++++++++++++------
 kernel/trace/trace.h  |  2 ++
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index c4cc048eb594..244e2d9083a6 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2860,6 +2860,8 @@ static void ftrace_shutdown_sysctl(void)
 
 static u64		ftrace_update_time;
 unsigned long		ftrace_update_tot_cnt;
+unsigned long		ftrace_number_of_pages;
+unsigned long		ftrace_number_of_groups;
 
 static inline int ops_traces_mod(struct ftrace_ops *ops)
 {
@@ -2984,6 +2986,9 @@ static int ftrace_allocate_records(struct ftrace_page *pg, int count)
 		goto again;
 	}
 
+	ftrace_number_of_pages += 1 << order;
+	ftrace_number_of_groups++;
+
 	cnt = (PAGE_SIZE << order) / ENTRY_SIZE;
 	pg->size = cnt;
 
@@ -3039,6 +3044,8 @@ ftrace_allocate_pages(unsigned long num_to_init)
 		start_pg = pg->next;
 		kfree(pg);
 		pg = start_pg;
+		ftrace_number_of_pages -= 1 << order;
+		ftrace_number_of_groups--;
 	}
 	pr_info("ftrace: FAILED to allocate memory for functions\n");
 	return NULL;
@@ -5788,6 +5795,8 @@ void ftrace_release_mod(struct module *mod)
 		free_pages((unsigned long)pg->records, order);
 		tmp_page = pg->next;
 		kfree(pg);
+		ftrace_number_of_pages -= 1 << order;
+		ftrace_number_of_groups--;
 	}
 }
 
@@ -6129,6 +6138,8 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr)
 			*last_pg = pg->next;
 			order = get_count_order(pg->size / ENTRIES_PER_PAGE);
 			free_pages((unsigned long)pg->records, order);
+			ftrace_number_of_pages -= 1 << order;
+			ftrace_number_of_groups--;
 			kfree(pg);
 			pg = container_of(last_pg, struct ftrace_page, next);
 			if (!(*last_pg))
@@ -6184,6 +6195,9 @@ void __init ftrace_init(void)
 				  __start_mcount_loc,
 				  __stop_mcount_loc);
 
+	pr_info("ftrace: allocated %ld pages with %ld groups\n",
+		ftrace_number_of_pages, ftrace_number_of_groups);
+
 	set_ftrace_early_filters();
 
 	return;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e917aa783675..bb41a70c5189 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7548,14 +7548,23 @@ static ssize_t
 tracing_read_dyn_info(struct file *filp, char __user *ubuf,
 		  size_t cnt, loff_t *ppos)
 {
-	unsigned long *p = filp->private_data;
-	char buf[64]; /* Not too big for a shallow stack */
+	unsigned long *p = ftrace_update_tot_cnt;
+	ssize_t ret;
+	char *buf;
 	int r;
 
-	r = scnprintf(buf, 63, "%ld", *p);
-	buf[r++] = '\n';
+	r = snprintf(NULL, 0, "%ld pages:%d groups: %d\n");
+	r++;
+	buf = kmalloc(r, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	r = scnprintf(buf, r, "%ld pages:%d groups: %d\n",
+		ftrace_update_tot_cnt,
+		ftrace_number_of_pages,
+		ftrace_number_of_groups);
 
-	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+	ret = simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
 static const struct file_operations tracing_dyn_info_fops = {
@@ -8747,7 +8756,7 @@ static __init int tracer_init_tracefs(void)
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 	trace_create_file("dyn_ftrace_total_info", 0444, d_tracer,
-			&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
+			NULL, &tracing_dyn_info_fops);
 #endif
 
 	create_trace_instances(d_tracer);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f801d154ff6a..f6f92a6c5cec 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -802,6 +802,8 @@ extern void trace_event_follow_fork(struct trace_array *tr, bool enable);
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 extern unsigned long ftrace_update_tot_cnt;
+extern unsigned long ftrace_number_of_pages;
+extern unsigned long ftrace_number_of_groups;
 void ftrace_init_trace_array(struct trace_array *tr);
 #else
 static inline void ftrace_init_trace_array(struct trace_array *tr) { }
-- 
2.20.1