Re: [PATCH v1] ring-buffer: Rename ring_buffer_size() to ring_buffer_capacity()

On Mon, Sep 07, 2026 at 11:41:46PM +0900, Masami Hiramatsu wrote:

On Mon,  7 Sep 2026 10:42:38 +0100
Vincent Donnefort [off-list ref] wrote:

quoted

Since commit 8a5f63637890 ("ring-buffer: Fix subbuf resize race with ring
buffer readers"), "capacity" refers to the memory available for events
(excluding subbuffer headers) while "size" refers to the raw allocation.
ring_buffer_size() actually calculates this event capacity. Rename it to
ring_buffer_capacity() to align with this convention.

I think this is OK, but I have a question.

[...]

quoted

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8658cad53cb5..f0251788ec75 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c

@@ -4712,9 +4712,9 @@ void trace_set_buffer_entries(struct array_buffer *buf, unsigned long val)
 static void update_buffer_entries(struct array_buffer *buf, int cpu)
 {
 	if (cpu == RING_BUFFER_ALL_CPUS) {
-		trace_set_buffer_entries(buf, ring_buffer_size(buf->buffer, 0));
+		trace_set_buffer_entries(buf, ring_buffer_capacity(buf->buffer, 0));
 	} else {
-		per_cpu_ptr(buf->data, cpu)->entries = ring_buffer_size(buf->buffer, cpu);
+		per_cpu_ptr(buf->data, cpu)->entries = ring_buffer_capacity(buf->buffer, cpu);

nit: Don't we need to re-word this "entries" with "capacity" too? 

Actually, this "entries" is a bit odd because

- ring_buffer_entries() returns the number of events.
- trace_set_buffer_entries() sets the buffer capacity in bytes.

It seems we call it as "entries" historical reason, but now it becomes the
source of confusion. Maybe we should change it too. (but in the separate patch)

Thanks,

Yes, I believe you're right, this "entries" here seems only used for
buffer_size_kb, buffer_total_size_kb and resize_buffer_duplicate_size() so we
can probably use "capacity" there too, it'll be less confusing than "entries".

I'll respin a v2 with that additional patch. (and a fix to the typo)

-- 
Vincent

quoted

 	}
 }
 

@@ -8476,7 +8476,7 @@ int allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int
 
 	/* Allocate the first page for all buffers */
 	trace_set_buffer_entries(&tr->array_buffer,
-				 ring_buffer_size(tr->array_buffer.buffer, 0));
+				 ring_buffer_capacity(tr->array_buffer.buffer, 0));
 
 	return 0;
 }

base-commit: df2908090cda368b01ff43709f51890076c56157
-- 
2.55.0.979.g7e5102b832-goog

-- 
Masami Hiramatsu (Google) [off-list ref]