linux-kernel - [PATCH v3 0/2] tracing: Make persistent ring buffer freeable

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Message-ID: <173928521419.906035.17750338150436695675.stgit@devnote2>
Date: Tue, 11 Feb 2025 23:46:54 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH v3 0/2] tracing: Make persistent ring buffer freeable

Hi,

Here is a pair of patches for making the persistent ring buffer
freeable. These were splitted from another series for improving
persistent ring buffer [1].

[1] https://lore.kernel.org/all/173920222697.826592.3726270716809214055.stgit@devnote2/

Anyway, this series allows us to release the memory for the persistent
ring buffer if it is not used anymore without changing kernel cmdline
and reboot. This allows us to enable the persistent ring buffer by
default boot, but disable it according to the user setting after boot
and recycle the memory for the persistent ring buffer.

This is important for the secure system which signs kernel cmdline with
the kernel image, because user can not change the cmdline easily
(usually, it is not possible unless changing kernel image.) Thus, to
use the persistent ring buffer, we need to enable it by default on such
system. However, in that case, some amount of memory is locked by the
persistent ring buffer even if it is not used by user setting.

This feature is useful for such case, because if user setting is
disabled the persistent tracing, we can release the persistent ring
buffer to free page pool.

Thank you,
---

Masami Hiramatsu (Google) (2):
      mm/memblock: Add reserved memory release function
      tracing: Freeable reserved ring buffer

 include/linux/mm.h   |    1 +
 kernel/trace/trace.c |   13 ++++++++-
 kernel/trace/trace.h |    1 +
 mm/memblock.c        |   72 ++++++++++++++++++++++++++++++++++++++++++--------
 4 files changed, 74 insertions(+), 13 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@...nel.org>