linux-kernel - Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

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Message-ID: <20241101174119.qso5fdln2chdflav@jpoimboe>
Date: Fri, 1 Nov 2024 10:41:19 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

On Thu, Oct 31, 2024 at 04:28:08PM -0700, Andrii Nakryiko wrote:
> So all task_structs on the system using 104 bytes more, *permanently*

Either way it's permanent, we don't know when to free it until the task
struct is freed...

> and *unconditionally*, is not a concern

Of course it's a concern, that's why we're looking for something
better...

> but lazy GFP_ATOMIC allocation when you actually need it is?

We don't want to dip into the GFP_ATOMIC emergency reserves, those are
kept for more important things.

Actually, I think I can just use GFP_NOWAIT here.

-- 
Josh