[PATCH] tracing: report buffer memory in /proc/meminfo

[Xiang Gao <gxxa03070307@gmail.com>]

Report the data capacity of all ftrace ring buffers through a new Ftrace
field in /proc/meminfo. Include the main and snapshot buffers of the
global trace array and all tracing instances, while leaving ring-buffer
metadata accounted for by Slab.

Keep the interface as a no-op when tracing is disabled so /proc/meminfo
does not gain a configuration dependency on tracing.

Tested on arm64 QEMU:

  CONFIG_TRACING=n:                   0 kB
  Global resize/restore:          7 -> 4099 -> 7 kB
  Instance and snapshot lifecycle: 15 -> 1434 -> 2836 -> 1434 -> 15 kB

Signed-off-by: Xiang Gao <gaoxiang17@xiaomi.com>
---
 fs/proc/meminfo.c     |  3 +++
 include/linux/trace.h |  5 +++++
 kernel/trace/trace.c  | 30 ++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index b2813ff13cb2..96a38ffc4e35 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -18,6 +18,7 @@
 #include <linux/cma.h>
 #endif
 #include <linux/zswap.h>
+#include <linux/trace.h>
 #include <asm/page.h>
 #include "internal.h"
 
@@ -108,6 +109,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 	show_val_kb(m, "Slab:           ", sreclaimable + sunreclaim);
 	show_val_kb(m, "SReclaimable:   ", sreclaimable);
 	show_val_kb(m, "SUnreclaim:     ", sunreclaim);
+	seq_printf(m, "Ftrace:         %8lu kB\n",
+		   ftrace_buffer_total_size() >> 10);
 	seq_printf(m, "KernelStack:    %8lu kB\n",
 		   global_node_page_state(NR_KERNEL_STACK_KB));
 #ifdef CONFIG_SHADOW_CALL_STACK
diff --git a/include/linux/trace.h b/include/linux/trace.h
index 7eaad857dee0..f9935231560c 100644
--- a/include/linux/trace.h
+++ b/include/linux/trace.h
@@ -53,6 +53,7 @@ int trace_array_init_printk(struct trace_array *tr);
 void trace_array_put(struct trace_array *tr);
 struct trace_array *trace_array_get_by_name(const char *name, const char *systems);
 int trace_array_destroy(struct trace_array *tr);
+unsigned long ftrace_buffer_total_size(void);
 
 /* For osnoise tracer */
 int osnoise_arch_register(void);
@@ -92,6 +93,10 @@ static inline int trace_array_destroy(struct trace_array *tr)
 {
 	return 0;
 }
+static inline unsigned long ftrace_buffer_total_size(void)
+{
+	return 0;
+}
 #endif	/* CONFIG_TRACING */
 
 #endif	/* _LINUX_TRACE_H */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 01a5e87af299..f0bb553e3688 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5769,6 +5769,36 @@ tracing_total_entries_read(struct file *filp, char __user *ubuf,
 	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
+static unsigned long trace_array_buffer_size(struct array_buffer *buf)
+{
+	unsigned long size = 0;
+	int cpu;
+
+	if (!buf->buffer)
+		return 0;
+
+	for_each_tracing_cpu(cpu)
+		size += ring_buffer_size(buf->buffer, cpu);
+
+	return size;
+}
+
+unsigned long ftrace_buffer_total_size(void)
+{
+	struct trace_array *tr;
+	unsigned long size = 0;
+
+	guard(mutex)(&trace_types_lock);
+	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+		size += trace_array_buffer_size(&tr->array_buffer);
+#ifdef CONFIG_TRACER_SNAPSHOT
+		size += trace_array_buffer_size(&tr->snapshot_buffer);
+#endif
+	}
+
+	return size;
+}
+
 #define LAST_BOOT_HEADER ((void *)1)
 
 static void *l_next(struct seq_file *m, void *v, loff_t *pos)
-- 
2.34.1