Re: [PATCH 0/2][RFC] [RFC] tracing: separate out buffer from trace_seq

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Steven Rostedt wrote:
> This is an RFC patch set. The trace_seq currently has its buffer
> within the structure itself. But this limits its ability and efficiency.
> 
> This patch set separates it out, but now it requires the callers
> to supply their own buffer. But this helps out the splice code because
> it can now write directly into the splice pages.
> 
> This may be too much for 33? But it is a nice fix.
> 
> Thoughs?
> 
> The following patches are in:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> 
>     branch: rfc/tracing/core
> 
> 
> Steven Rostedt (2):
>       tracing: Change trace_seq to use separate buffer
>       tracing: Write directly into splice page for trace_pipe

It's great that you wrote it and trace_pipe benefit from it.
And it show separate buffer is required.

But I didn't expect so much/big changes. I'm wondering that
we can use seq file directly for some files and
kill all kmalloc(sizeof(struct trace_seq)).

kernel/trace/trace.c:3720:      s = kmalloc(sizeof(*s), GFP_KERNEL);
We can use a short buffer + simple_read_from_buffer()
Or seq file.

kernel/trace/trace_events.c:539:        s = kmalloc(sizeof(*s), GFP_KERNEL);
We can use seq file after of my patchset(today) is applied.

kernel/trace/trace_events.c:580:        s = kmalloc(sizeof(*s), GFP_KERNEL);
we can use a shor buffer. "char buf[20]" + simple_read_from_buffer()

kernel/trace/trace_events.c:604:        s = kmalloc(sizeof(*s), GFP_KERNEL);
We can use a short buffer + simple_read_from_buffer()
Or seq file.

kernel/trace/trace_events.c:660:        s = kmalloc(sizeof(*s), GFP_KERNEL);
We can use a short buffer + simple_read_from_buffer()
Or seq file.

kernel/trace/trace_events.c:715:        s = kmalloc(sizeof(*s), GFP_KERNEL);
We can use seq file.

kernel/trace/trace_ksym.c:230:  s = kmalloc(sizeof(*s), GFP_KERNEL);
We should use seq! It's very bad that we use trace_seq.

For function_stat_show(), it uses static trace_seq. but it can also
use a short buffer + simple_read_from_buffer().

I will do this.(or you if you would like to)

So could you write a simpler version of separate-buffer-trace_seq
with supposition that all kmalloc(sizeof(struct trace_seq)) are removed.

Lai.

> 
> ----
>  include/linux/ftrace_event.h |    6 ++++-
>  include/linux/trace_seq.h    |   22 +++++++++++++++-
>  include/trace/ftrace.h       |   20 +++++++++++----
>  kernel/trace/ftrace.c        |    3 +-
>  kernel/trace/trace.c         |   54 ++++++++++++++++-------------------------
>  kernel/trace/trace_events.c  |   45 +++++++++++++++++++++++++++++++----
>  kernel/trace/trace_ksym.c    |   10 +++++++-
>  kernel/trace/trace_output.c  |   24 ++++++++++--------
>  8 files changed, 125 insertions(+), 59 deletions(-)
> 
> 
>