On Fri, Sep 11, 2026 at 11:50:16PM +0800, Xiang Gao wrote:
> + /* The cached read page, if present, is a full sub-buffer page. */
> + if (cpu_buffer->free_page)
> + size += subbuf_size;
Have you compile-tested this one? free_page is a struct, not a pointer:
kernel/trace/ring_buffer.c:6594:13: error: used struct type value where
scalar is required
6594 | if (cpu_buffer->free_page)
| ^~~~~~~~~~
cpu_buffer->free_page.data should do it.
> + list_for_each_entry(tr, &ftrace_trace_arrays, list) {
> + for_each_tracing_cpu(cpu)
> + trace_array_buffer_memory(tr, cpu, &stats.buffers,
> + &stats.snapshot);
> + }
With that fixed the walk does match the changelog, but temp_buffer is out
of its reach. tracer_alloc_buffers() allocates it and never attaches it to
a trace array, so it is not on ftrace_trace_arrays, and its pages are the
kind you are counting: sub-buffers and a reader page from the page
allocator, not remote and not slab.
It is three sub-buffers per CPU at order 0 and is never resized, so it
disappears into the noise once a real buffer is sized up. At rest it does
not. On an 8 CPU x86_64 guest the file reports
buffers: 96
while temp_buffer holds another 96K. Freeing it hands back 24 pages, which
is what ring_buffer_memory_size() predicts for it.
Was that deliberate? For lost RAM accounting I would have expected it in.
