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Date: Wed, 18 Jun 2025 16:01:11 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
	bpf@vger.kernel.org, x86@kernel.org,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Ingo Molnar <mingo@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrii Nakryiko <andrii@kernel.org>,
	Indu Bhagat <indu.bhagat@oracle.com>,
	"Jose E. Marchesi" <jemarch@gnu.org>,
	Beau Belgrave <beaub@linux.microsoft.com>,
	Jens Remus <jremus@linux.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v10 04/14] unwind_user/deferred: Add
 unwind_deferred_trace()
Message-ID: <20250618140111.GP1613376@noisy.programming.kicks-ass.net>
References: <20250611005421.144238328@goodmis.org>
 <20250611010428.433111891@goodmis.org>
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In-Reply-To: <20250611010428.433111891@goodmis.org>

On Tue, Jun 10, 2025 at 08:54:25PM -0400, Steven Rostedt wrote:

> +#define UNWIND_MAX_ENTRIES 512

The reason this is 512 is so that you end up with a whole page below?

> +int unwind_deferred_trace(struct unwind_stacktrace *trace)
> +{
> +	struct unwind_task_info *info = &current->unwind_info;
> +
> +	/* Should always be called from faultable context */
> +	might_fault();
> +
> +	if (current->flags & PF_EXITING)
> +		return -EINVAL;
> +
> +	if (!info->entries) {
> +		info->entries = kmalloc_array(UNWIND_MAX_ENTRIES, sizeof(long),
> +					      GFP_KERNEL);