linux-kernel - Re: [PATCH] debugobjects: add a new Kconfig for POOL

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Message-ID: <44517d7f-c34f-1424-d0db-601e590c626d@redhat.com>
Date:   Mon, 19 Nov 2018 09:51:16 -0500
From:   Waiman Long <longman@...hat.com>
To:     Qian Cai <cai@....us>, Thomas Gleixner <tglx@...utronix.de>
Cc:     linux kernel <linux-kernel@...r.kernel.org>, arnd@...db.de,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: Re: [PATCH] debugobjects: add a new Kconfig for POOL_SIZE

On 11/19/2018 08:27 AM, Qian Cai wrote:
> On 11/19/18 at 3:09 AM, Thomas Gleixner wrote:
>
>> Qian,
>>
>> On Sun, 18 Nov 2018, Qian Cai wrote:
>>>> On Nov 18, 2018, at 1:21 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>>>> On Sun, 18 Nov 2018, Qian Cai wrote:
>>>>> As the results, systems have 60+ CPUs with both timer and workqueue
>>>>> objects enabled could trigger "ODEBUG: Out of memory. ODEBUG disabled".
>>>>>
>>>>> Hence, add a new Kconfig option so users could adjust ODEBUG_POOL_SIZE
>>>>> accordingly if either timer or workqueue objects are selected.
>>>> why do we need a config option, when the required number can be deduced
>>>> already from the active CONFIG_DEBUG_OBJECTS_* and NR_CPUS?
>>>>
>>> It because I am worry about the coupling between the implementation details of
>>> timers and workqueue objects, and the computation in the code you mentioned
>>> here. For example, people could change workqueue.c to have different number
>>> of worekqueues initialized during the early boot in the future which is going to
>>> affect the required pool size, and I am not sure if people are going to adjust the
>>> code in debugobjects.c here as well when they made changes like that.
>>>
>>> Also, the computation could become so complex depends on lots of config
>>> options like perf, hrtimer, and combinations that I have not tested so far which is
>>> difficult to exhausted all the possibilities.
>>>
>>> Hence, I feel like the Kconfig option is more flexible and less error-prone.
>> Quite the contrary. Config options are a pain and truly error-prone if you
>> want to compile general purpose kernels as distributions do.
>>
> Ah, I never thought distributions people would
> enable those debugging options.

Distros like RHEL usually ship two kernels - one for production and one
for debug. The debug kernel does have debugobjects enabled.

Cheers,
Longman