linux-kernel - Re: [RFC PATCH 3/5] unwind deferred: Introduce unwind_user_trace

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Message-ID: <aHC_PFyC11ewcdB_@infradead.org>
Date: Fri, 11 Jul 2025 00:37:32 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 3/5] unwind deferred: Introduce
 unwind_user_trace_cached

On Wed, Jul 09, 2025 at 05:25:50PM -0400, Mathieu Desnoyers wrote:
> Introduce unwind_user_trace_cached which copies the stack trace if it
> was previously stored into the cache since the last reset of the cache.
> 
> The expected use-case is sampling a stack trace from a faultable context
> at system call entry (coping it into the cache), and then copying the
> stack trace from the cache from non-faultable context to a ring buffer.

Why is this and the following patches adding unused code?