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

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Date:   Mon, 19 Nov 2018 09:09:16 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Qian Cai <cai@....us>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Waiman Long <longman@...hat.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>, arnd@...db.de,
        linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] debugobjects: add a new Kconfig for POOL_SIZE

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.

Its not really a problem to have a larger initial static pool which gets
freed after init anyway. So we can size it generously depending on the
config options and be done with it.

Thanks,

	tglx