linux-kernel - Re: [PATCH v6 5/6] tracing: Show inode and device major:minor in deferred user space stacktrace

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Message-ID: <CAHk-=wh8QVL4rb_17+6NfxW=AF-HS0WarMmq-nYm42akG0-Gbg@mail.gmail.com>
Date: Fri, 29 Aug 2025 13:54:08 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>, Steven Rostedt <rostedt@...nel.org>, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>, 
	Indu Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>, 
	Beau Belgrave <beaub@...ux.microsoft.com>, Jens Remus <jremus@...ux.ibm.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Florian Weimer <fweimer@...hat.com>, 
	Sam James <sam@...too.org>, Kees Cook <kees@...nel.org>, "Carlos O'Donell" <codonell@...hat.com>
Subject: Re: [PATCH v6 5/6] tracing: Show inode and device major:minor in
 deferred user space stacktrace

On Fri, 29 Aug 2025 at 11:11, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> The idea is this (pseudo code):
>
>  user_stack_trace() {
>    foreach vma in each stack frame:
>        key = hash(vma->vm_file);
>        if (!lookup(key)) {
>            trace_file_map(key, generate_path(vma), generate_buildid(vma));
>            add_into_hash(key);
>        }
>    }

I see *zero* advantage to this. It's only doing stupid things that
cost extra, and only because you don't want to do the smart thing that
I've explained extensively that has *NONE* of these overheads.

Just do the parsing at parse time. End of story.

Or don't do this at all. Justy forget the whole thing entirely. Throw
the patch that started this all away, and just DON'T DO THIS.

              Linus