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Date:   Sun, 28 Jun 2020 15:00:15 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Nicolas Boichat <drinkcat@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Peter Zijlstra <peterz@infradead.org>,
        Vinod Koul <vkoul@kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Guilherme G . Piccoli" <gpiccoli@canonical.com>,
        Will Deacon <will@kernel.org>,
        Douglas Anderson <dianders@chromium.org>,
        Guenter Roeck <groeck@chromium.org>, bpf@vger.kernel.org
Subject: Re: [PATCH] kernel/trace: Add TRACING_ALLOW_PRINTK config option
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On Sun, 28 Jun 2020 14:46:16 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> > We added a bunch of code to libbcc in the past to support instances,
> > but eventually removed it all due to memory overhead per instance.
> > If I recall it was ~8Mbyte per instance. That was couple years ago.  
> 
> I'd like to see where that 8 MB per instance came from. You can control
> the size of the instance buffers. If size is still an issue, I'll be
> happy to work with you to fix it.

Looks to be the duplication of the event directory tree. There's a lot
of duplicate data there. Instead of just punting and saying "instances
are too large" perhaps you could get someone to look at a way to
consolidate that data? I'm sure there's a lot of ways to help here.

Or you can just create a new event called bpf_printk() that passes in
and records a string and enable that automatically when a bpf module
has it. That could work as well.

In either case, your use of trace_printk() is an abuse of its purpose.

-- Steve