From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Sachin Sant <sachinp@linux.ibm.com>
Subject: Re: [PATCH] tracing: Limit trace_seq size to just 8K and not depend on architecture PAGE_SIZE
Date: Thu, 11 Apr 2024 08:12:58 +0900 [thread overview]
Message-ID: <20240411081258.d96952359c857461278d6559@kernel.org> (raw)
In-Reply-To: <20240304191342.56fb1087@gandalf.local.home>
On Mon, 4 Mar 2024 19:13:42 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
>
> The trace_seq buffer is used to print out entire events. It's typically
> set to PAGE_SIZE * 2 as there's some events that can be quite large.
>
> As a side effect, writes to trace_marker is limited by both the size of the
> trace_seq buffer as well as the ring buffer's sub-buffer size (which is a
> power of PAGE_SIZE). By limiting the trace_seq size, it also limits the
> size of the largest string written to trace_marker.
>
> trace_seq does not need to be dependent on PAGE_SIZE like the ring buffer
> sub-buffers need to be. Hard code it to 8K which is PAGE_SIZE * 2 on most
> architectures. This will also limit the size of trace_marker on those
> architectures with greater than 4K PAGE_SIZE.
>
> Link: https://lore.kernel.org/all/20240302111244.3a1674be@gandalf.local.home/
>
8K is reasonably enough big. Looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Thank you,
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> include/linux/trace_seq.h | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
> index 9ec229dfddaa..1ef95c0287f0 100644
> --- a/include/linux/trace_seq.h
> +++ b/include/linux/trace_seq.h
> @@ -9,9 +9,15 @@
> /*
> * Trace sequences are used to allow a function to call several other functions
> * to create a string of data to use.
> + *
> + * Have the trace seq to be 8K which is typically PAGE_SIZE * 2 on
> + * most architectures. The TRACE_SEQ_BUFFER_SIZE (which is
> + * TRACE_SEQ_SIZE minus the other fields of trace_seq), is the
> + * max size the output of a trace event may be.
> */
>
> -#define TRACE_SEQ_BUFFER_SIZE (PAGE_SIZE * 2 - \
> +#define TRACE_SEQ_SIZE 8192
> +#define TRACE_SEQ_BUFFER_SIZE (TRACE_SEQ_SIZE - \
> (sizeof(struct seq_buf) + sizeof(size_t) + sizeof(int)))
>
> struct trace_seq {
> --
> 2.43.0
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
prev parent reply other threads:[~2024-04-10 23:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-05 0:13 [PATCH] tracing: Limit trace_seq size to just 8K and not depend on architecture PAGE_SIZE Steven Rostedt
2024-04-10 23:12 ` Masami Hiramatsu [this message]
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