linux-kernel - Re: [PATCH 2/2] tracing: Resize tgid_map to PID_MAX_LIMIT, not PID_MAX

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Message-ID: <20210630083513.1658a6fb@oasis.local.home>
Date:   Wed, 30 Jun 2021 08:35:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Paul Burton <paulburton@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] tracing: Resize tgid_map to PID_MAX_LIMIT, not
 PID_MAX_DEFAULT

On Tue, 29 Jun 2021 17:34:06 -0700
Paul Burton <paulburton@...gle.com> wrote:

> On 64 bit systems this will increase the size of tgid_map from 256KiB to
> 16MiB. Whilst this 64x increase in memory overhead sounds significant 64
> bit systems are presumably best placed to accommodate it, and since
> tgid_map is only allocated when the record-tgid option is actually used
> presumably the user would rather it spends sufficient memory to actually
> record the tgids they expect.

NAK. Please see how I fixed this for the saved_cmdlines, and implement
it the same way.

785e3c0a3a87 ("tracing: Map all PIDs to command lines")

It's a cache, it doesn't need to save everything.

-- Steve


> 
> The size of tgid_map will also increase for CONFIG_BASE_SMALL=y
> configurations, but these seem unlikely to be systems upon which people
> are running ftrace with record-tgid anyway.