linux-kernel - Re: [PATCH] percpu: improve percpu_alloc_percpu

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Date: Wed, 24 Jan 2024 00:13:11 -0800
From: Dennis Zhou <dennis@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>,
	George Guo <dongtai.guo@...ux.dev>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	George Guo <guodongtai@...inos.cn>, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] percpu: improve percpu_alloc_percpu_fail event trace

Hello,

On Mon, Jan 22, 2024 at 08:55:39PM -0500, Steven Rostedt wrote:
> On Tue, 23 Jan 2024 09:44:43 +0800
> George Guo <dongtai.guo@...ux.dev> wrote:
> 
> > There are two reasons of percpu_alloc failed without warnings: 
> > 
> > 1. do_warn is false
> > 2. do_warn is true and warn_limit is reached the limit.
> 
> Yes I know the reasons.
> 
> > 
> > Showing do_warn and warn_limit makes things simple, maybe dont need
> > kprobe again.
> 
> It's up to the maintainers of that code to decide if it's worth it or not,
> but honestly, my opinion it is not.
> 

I agree, I don't think this is a worthwhile change. If we do change
this, I'd like it to be more actionable in some way and as a result
something we can fix or tune accordingly.

George is this a common problem you're seeing?

> The trace event in question is to trace that percpu_alloc failed and why.
> It's not there to determine why it did not produce a printk message.
> 
> -- Steve

Thanks,
Dennis