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Message-ID: <889b1a2849f50eeda2b334a7045c6748449d3d38.camel@linux.intel.com>
Subject: Re: [PATCH v2] tracing: Have saved_cmdlines arrays all in one
 allocation
From: Tim Chen <tim.c.chen@linux.intel.com>
To: Steven Rostedt <rostedt@goodmis.org>, LKML
 <linux-kernel@vger.kernel.org>,  Linux Trace Kernel
 <linux-trace-kernel@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@efficios.com>, Mark Rutland <mark.rutland@arm.com>, 
 Vincent Donnefort <vdonnefort@google.com>, Sven Schnelle
 <svens@linux.ibm.com>, Mete Durlu <meted@linux.ibm.com>
Date: Tue, 13 Feb 2024 16:09:56 -0800
In-Reply-To: <20240213115232.5fd9e611@gandalf.local.home>
References: <20240213115232.5fd9e611@gandalf.local.home>
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On Tue, 2024-02-13 at 11:52 -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
>=20
> The saved_cmdlines have three arrays for mapping PIDs to COMMs:
>=20
>  - map_pid_to_cmdline[]
>  - map_cmdline_to_pid[]
>  - saved_cmdlines
>=20
> The map_pid_to_cmdline[] is PID_MAX_DEFAULT in size and holds the index
> into the other arrays. The map_cmdline_to_pid[] is a mapping back to the
> full pid as it can be larger than PID_MAX_DEFAULT. And the
> saved_cmdlines[] just holds the COMMs associated to the pids.
>=20
> Currently the map_pid_to_cmdline[] and saved_cmdlines[] are allocated
> together (in reality the saved_cmdlines is just in the memory of the
> rounding of the allocation of the structure as it is always allocated in
> powers of two). The map_cmdline_to_pid[] array is allocated separately.
>=20
> Since the rounding to a power of two is rather large (it allows for 8000
> elements in saved_cmdlines), also include the map_cmdline_to_pid[] array.
> (This drops it to 6000 by default, which is still plenty for most use
> cases). This saves even more memory as the map_cmdline_to_pid[] array
> doesn't need to be allocated.
>=20
> Link: https://lore.kernel.org/linux-trace-kernel/20240212174011.068211d9@=
gandalf.local.home/
>=20
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>


Patch looks good to me.

Reviewd-by: Tim Chen <tim.c.chen@linux.intel.com>

> ---
> Changes since v1: https://lore.kernel.org/linux-trace-kernel/202402121809=
41.379c419b@gandalf.local.home/
>=20
> -- Added SAVED_CMDLINE_MAP_ELEMENT_SIZE helper macro.
>=20