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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-485885be1c1sm26508442f8f.32.2026.09.07.02.26.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Sep 2026 02:26:33 -0700 (PDT) Date: Mon, 7 Sep 2026 10:26:30 +0100 From: Vincent Donnefort To: Xiang Gao Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Lorenzo Stoakes , gao xu , yinchuang1@xiaomi.com, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Xiang Gao Subject: Re: [PATCH 1/2] tracing: add ring-buffer memory usage statistics in tracefs Message-ID: References: <20260905112732.3705405-1-gaoxiang17@xiaomi.com> <20260905112732.3705405-2-gaoxiang17@xiaomi.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260905112732.3705405-2-gaoxiang17@xiaomi.com> On Sat, Sep 05, 2026 at 07:27:31PM +0800, Xiang Gao wrote: > Report the memory consumed by the tracing ring buffers, rather than the > usable data capacity exposed by buffer_size_kb. Android low-memory > diagnostics need this to attribute the memory used by tracing when > calculating lost RAM. > > The buffers can be spread across the global trace array, dynamically > created instances, and snapshot buffers. Userspace currently has to > discover and sum every instance, and snapshot memory is not exposed by > the per-instance totals. > > Add a trace_stats directory with memory_usage_kb reporting: > > buffers: > snapshot_buffers: > > covering the global trace array and all instances across all CPUs. > > The values account for the full pages backing the data sub-buffers and > reader page, plus the cached read page and mmap metadata page when > present. Slab-allocated ring-buffer metadata is not included, as it is > already reported through Slab and would be double-counted when > subtracting tracing memory from lost RAM. Range and remote buffers, > whose pages are externally owned, report zero. > > Signed-off-by: Xiang Gao > --- > Documentation/trace/ftrace.rst | 12 +++++++ > include/linux/ring_buffer.h | 1 + > kernel/trace/ring_buffer.c | 41 +++++++++++++++++++++++ > kernel/trace/trace.c | 60 ++++++++++++++++++++++++++++++++++ > 4 files changed, 114 insertions(+) > > diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst > index 84f06bf0da9b..ff9d604dd1b8 100644 > --- a/Documentation/trace/ftrace.rst > +++ b/Documentation/trace/ftrace.rst > @@ -218,6 +218,18 @@ of ftrace. Here is a list of some of the key files: > > This displays the total combined size of all the trace buffers. > > + trace_stats/memory_usage_kb: > + > + This reports the memory consumed by the ring buffers, as opposed to > + the usable data capacity shown by buffer_size_kb. The value covers the > + main and snapshot buffers of the global trace array and all tracing > + instances. It does not include slab-allocated ring-buffer metadata. > + > + Output:: > + > + buffers: ... > + snapshot_buffers: ... > + > buffer_subbuf_size_kb: > > This sets or displays the sub buffer size. The ring buffer is broken up > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h > index 0670742b2d60..64eded40222c 100644 > --- a/include/linux/ring_buffer.h > +++ b/include/linux/ring_buffer.h > @@ -166,6 +166,7 @@ int ring_buffer_iter_empty(struct ring_buffer_iter *iter); > bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter); > > unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu); > +unsigned long ring_buffer_memory_size(struct trace_buffer *buffer, int cpu); > unsigned long ring_buffer_max_event_size(struct trace_buffer *buffer); > > void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu); > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 8e2485bb3aa8..a8719b517798 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -6464,6 +6464,47 @@ unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu) > } > EXPORT_SYMBOL_GPL(ring_buffer_size); > > +/** > + * ring_buffer_memory_size - return the memory used by the buffer (in bytes) > + * @buffer: The ring buffer. > + * @cpu: The CPU to get ring buffer memory from. > + * > + * Returns the page-allocator memory consumed by @cpu, including the data > + * sub-buffers, the reader page, the cached read page, and the mmap > + * metadata page. Unlike ring_buffer_size(), which reports the usable data > + * capacity, this accounts for the full pages allocated to the buffer. > + * Range and remote buffers do not own page-allocator memory and report zero. > + */ > +unsigned long ring_buffer_memory_size(struct trace_buffer *buffer, int cpu) > +{ > + struct ring_buffer_per_cpu *cpu_buffer; > + unsigned long subbuf_size; > + unsigned long size; > + > + if (!cpumask_test_cpu(cpu, buffer->cpumask)) > + return 0; > + > + /* Range and remote buffers use externally owned memory. */ > + if (buffer->range_addr_start || buffer->remote) > + return 0; Hum, why not including that? This is still memory immobilised for tracing. (notice though remote buffers wouldn't appear in ftrace_trace_arrays) > + > + cpu_buffer = buffer->buffers[cpu]; > + subbuf_size = PAGE_SIZE << buffer->subbuf_order; READ_ONCE(buffer->subbuf_order); > + > + /* Data sub-buffers plus the reader page. */ > + size = (cpu_buffer->nr_pages + 1) * subbuf_size; > + > + /* The cached read page, if present, is a full sub-buffer page. */ > + if (cpu_buffer->free_page) > + size += subbuf_size; > + > + /* The mmap metadata page is a single system page. */ > + if (cpu_buffer->meta_page) > + size += PAGE_SIZE; > + > + return size; > +} > + > /** > * ring_buffer_max_event_size - return the max data size of an event > * @buffer: The ring buffer. > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 01a5e87af299..b343e03a6cf8 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -5769,6 +5769,52 @@ tracing_total_entries_read(struct file *filp, char __user *ubuf, > return simple_read_from_buffer(ubuf, cnt, ppos, buf, r); > } > > +struct trace_mem_stats { > + unsigned long buffers; > + unsigned long snapshot; > +}; > + > +static void > +trace_array_buffer_memory(struct trace_array *tr, int cpu, > + unsigned long *buffers, unsigned long *snapshot) > +{ > + if (tr->array_buffer.buffer) > + *buffers += ring_buffer_memory_size(tr->array_buffer.buffer, cpu); > + > +#ifdef CONFIG_TRACER_SNAPSHOT > + if (tr->snapshot_buffer.buffer) > + *snapshot += ring_buffer_memory_size(tr->snapshot_buffer.buffer, cpu); > +#endif > +} > + > +static struct trace_mem_stats trace_buffers_memory(void) > +{ > + struct trace_mem_stats stats = {}; > + struct trace_array *tr; > + int cpu; > + > + guard(mutex)(&trace_types_lock); > + > + list_for_each_entry(tr, &ftrace_trace_arrays, list) { > + for_each_tracing_cpu(cpu) > + trace_array_buffer_memory(tr, cpu, &stats.buffers, > + &stats.snapshot); > + } > + > + return stats; > +} > + > +static int trace_mem_show(struct seq_file *m, void *v) > +{ > + struct trace_mem_stats stats = trace_buffers_memory(); > + > + seq_printf(m, "buffers: %lu\n", stats.buffers >> 10); > + seq_printf(m, "snapshot_buffers: %lu\n", stats.snapshot >> 10); > + > + return 0; > +} > +DEFINE_SHOW_ATTRIBUTE(trace_mem); > + > #define LAST_BOOT_HEADER ((void *)1) > > static void *l_next(struct seq_file *m, void *v, loff_t *pos) > @@ -9188,6 +9234,18 @@ static struct notifier_block trace_module_nb = { > }; > #endif /* CONFIG_MODULES */ > > +static __init void init_trace_stats_tracefs(void) > +{ > + struct dentry *stats_dir; > + > + stats_dir = tracefs_create_dir("trace_stats", NULL); > + if (!stats_dir) > + return; > + > + trace_create_file("memory_usage_kb", TRACE_MODE_READ, stats_dir, > + NULL, &trace_mem_fops); > +} > + > static __init void tracer_init_tracefs_work_func(struct work_struct *work) > { > > @@ -9196,6 +9254,8 @@ static __init void tracer_init_tracefs_work_func(struct work_struct *work) > init_tracer_tracefs(&global_trace, NULL); > ftrace_init_tracefs_toplevel(&global_trace, NULL); > > + init_trace_stats_tracefs(); > + > trace_create_file("tracing_thresh", TRACE_MODE_WRITE, NULL, > &global_trace, &tracing_thresh_fops); > > -- > 2.34.1 > >