linux-kernel - [PATCH v5 01/25] ring-buffer: Add page statistics to the meta-page

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Message-ID: <20250516134031.661124-2-vdonnefort@google.com>
Date: Fri, 16 May 2025 14:40:07 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com, 
	linux-trace-kernel@...r.kernel.org, maz@...nel.org, oliver.upton@...ux.dev, 
	joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com
Cc: kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	jstultz@...gle.com, qperret@...gle.com, will@...nel.org, 
	kernel-team@...roid.com, linux-kernel@...r.kernel.org, 
	Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH v5 01/25] ring-buffer: Add page statistics to the meta-page

Add two fields pages_touched and pages_lost to the ring-buffer
meta-page. Those fields are useful to get the number of used pages in
the ring-buffer.

Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>

diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
index c102ef35d11e..e8185889a1c8 100644
--- a/include/uapi/linux/trace_mmap.h
+++ b/include/uapi/linux/trace_mmap.h
@@ -17,8 +17,8 @@
  * @entries:		Number of entries in the ring-buffer.
  * @overrun:		Number of entries lost in the ring-buffer.
  * @read:		Number of entries that have been read.
- * @Reserved1:		Internal use only.
- * @Reserved2:		Internal use only.
+ * @pages_lost:		Number of pages overwritten by the writer.
+ * @pages_touched:	Number of pages written by the writer.
  */
 struct trace_buffer_meta {
 	__u32		meta_page_size;
@@ -39,8 +39,8 @@ struct trace_buffer_meta {
 	__u64	overrun;
 	__u64	read;
 
-	__u64	Reserved1;
-	__u64	Reserved2;
+	__u64	pages_lost;
+	__u64	pages_touched;
 };
 
 #define TRACE_MMAP_IOCTL_GET_READER		_IO('R', 0x20)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3f9bf562beea..06214588c05a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6016,6 +6016,8 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 	meta->entries = local_read(&cpu_buffer->entries);
 	meta->overrun = local_read(&cpu_buffer->overrun);
 	meta->read = cpu_buffer->read;
+	meta->pages_lost = local_read(&cpu_buffer->pages_lost);
+	meta->pages_touched = local_read(&cpu_buffer->pages_touched);
 
 	/* Some archs do not have data cache coherency between kernel and user-space */
 	flush_kernel_vmap_range(cpu_buffer->meta_page, PAGE_SIZE);
-- 
2.49.0.1101.gccaa498523-goog