Re: [PATCH v2] tracing: Have saved_cmdlines arrays all in one allocation

[Tim Chen]

On Tue, 2024-02-13 at 11:52 -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
> 
> The saved_cmdlines have three arrays for mapping PIDs to COMMs:
> 
>  - map_pid_to_cmdline[]
>  - map_cmdline_to_pid[]
>  - saved_cmdlines
> 
> 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.
> 
> 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.
> 
> 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.
> 
> Link: https://lore.kernel.org/linux-trace-kernel/20240212174011.068211d9@xxxxxxxxxxxxxxxxxx/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>


Patch looks good to me.

Reviewd-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>

> ---
> Changes since v1: https://lore.kernel.org/linux-trace-kernel/20240212180941.379c419b@xxxxxxxxxxxxxxxxxx/
> 
> -- Added SAVED_CMDLINE_MAP_ELEMENT_SIZE helper macro.
>