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: <20250829124922.6826cfe6@gandalf.local.home>
Date: Fri, 29 Aug 2025 12:49:22 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...nel.org>, Arnaldo Carvalho de Melo
 <arnaldo.melo@...il.com>, 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 09:28:41 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Don't try to "reuse" hashes. Just treat them as opaque numbers.

What do I use to make the hash?

One thing this is trying to do is not have to look up the path name for
every line of a stack trace.

I could just have every instance do the full look up, make a hash from the
path name and build id, and pass the hash to the caller. My worry is the
time it takes to generate that.

Perhaps I could have a hash that maps the pid with the vma->vm_start, and
if that's unique, get the path and build-id and create the hash for that
and send it back to the user. Save the hash for that mapping in the
rhashtable with the pid/vm_start as the key.

Then the code that adds the vma, will see if the pid/vma->start exists, if
it does, return the hash associated with that, if it does not, add it and
trigger the event that a new address has been created.

-- Steve