linux-kernel - Re: [PATCH] ftrace: fix task's invalid comm of <...> when big pid

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Message-ID: <6ea3f860-c7ae-6400-3f15-842a06f20ae8@linux.alibaba.com>
Date:   Fri, 30 Mar 2018 16:21:31 +0800
From:   Wang Yu <yuwang@...ux.alibaba.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: fix task's invalid comm of <...> when big pid



在 18/3/29 下午10:26, Steven Rostedt 写道:
> On Thu, 29 Mar 2018 10:16:22 +0800
> Wang Yu <yuwang@...ux.alibaba.com> wrote:
>
>>> What you can do is make that map_pid_to_cmdline array bigger.
>>>
>>> -- Steve
>> I am sorry about it, and as the number of cpu cores increases, the current
>>
>> PID_MAX_DEFAULT is too small, our online machines set the pid_max 65536 as default, so the task
>> pid number bigger than PID_MAX_DEFAULT can't show the real comm (only <...>), so i want to
>> ajust the PID_MAX_DEFAULT upto 4x, and what do you think?
>>
>>     * This controls the default maximum pid allocated to a process
>>     */
>> -#define PID_MAX_DEFAULT (CONFIG_BASE_SMALL ? 0x1000 : 0x8000)
>> +#define PID_MAX_DEFAULT (CONFIG_BASE_SMALL ? 0x1000 : 0x20000)
> What I was thinking is to make the map_pid_to_cmdline array dynamic
> (not static), and be set to pid_max (after pid_max is determined).
>
> Now, pid_max can be changed at run time. Thus, the tracing code will
> need to keep a separate variable for that array to store the length. It
> can not rely on pid_max. But if a pid that is greater than pid_max is
> found, we could kick off a work thread to increase the array.
thanks for your reply, thanks, if map_pid_to_cmdline need dynamic, 
saved_cmdlines_buffer