linux-kernel - Re: [PATCH 00/14] xfs: Remove unused trace events

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Message-ID: <20250616053119.GD1148@lst.de>
Date: Mon, 16 Jun 2025 07:31:19 +0200
From: Christoph Hellwig <hch@....de>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: "Darrick J. Wong" <djwong@...nel.org>, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Carlos Maiolino <cem@...nel.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 00/14] xfs: Remove unused trace events

On Fri, Jun 13, 2025 at 11:31:19AM -0400, Steven Rostedt wrote:
> On Fri, 13 Jun 2025 08:08:55 -0700
> "Darrick J. Wong" <djwong@...nel.org> wrote:
> 
> > On Thu, Jun 12, 2025 at 05:24:05PM -0400, Steven Rostedt wrote:
> > > 
> > > Trace events take up to 5K in memory for text and meta data. I have code that  
> > 
> > Under what circumstances do they eat up that much memory?  And is that
> > per-class?  Or per-tracepoint?
> 
> I just did an analysis of this:
> 
>   https://lore.kernel.org/lkml/20250613104240.509ff13c@batman.local.home/T/#md81abade0df19ba9062fd51ced4458161f885ac3
> 
> A TRACE_EVENT() is about 5K, and each DEFINE_EVENT() is about 1K.

That's really quite expensive.  And you only measured the tezt/data/bss
overhead and not even the dynamic memory overhead, which is probably
a lot more.