linux-kernel - Re: [PATCH v2 7/7] mm/tracing: introduce max_vma_count

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Message-ID: <20250916115220.4a90c745@batman.local.home>
Date: Tue, 16 Sep 2025 11:52:20 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Kalesh Singh <kaleshsingh@...gle.com>
Cc: akpm@...ux-foundation.org, minchan@...nel.org,
 lorenzo.stoakes@...cle.com, david@...hat.com, Liam.Howlett@...cle.com,
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 android-mm@...gle.com, Alexander Viro <viro@...iv.linux.org.uk>, Christian
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 <kees@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan
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 <shuah@...nel.org>, linux-kernel@...r.kernel.org,
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 linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 7/7] mm/tracing: introduce max_vma_count_exceeded
 trace event

On Mon, 15 Sep 2025 18:19:53 -0700
Kalesh Singh <kaleshsingh@...gle.com> wrote:


> Hi Steve,
> 
> Thanks for the comments and suggestion you are right we can use bpf to
> get the comm. There is nothing special about this trace event.  I will
> drop comm in the next revision.
> 
> The reason I did the task_struct parameter (current): I believe there
> is a limitation that we must  specify at least 1 parameter to the
> TRACE_EVENT()  PROTO and ARGS macros.

OK, then this is another issue. We don't want tracepoint "markers".
Each tracepoint can take up to 5K in memory due to the code it
generates and the meta data to control it.

For something like that, we highly recommend dynamic probes (fprobes,
kprobes, etc).

The only purpose of a static tracepoint is to get data within a
function that is too difficult to get via a probe. It should never be
used as a trigger where its purpose is "we hit this path".

-- Steve