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

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Date:   Mon, 19 Nov 2018 14:27:37 +0100
From:   "Qian Cai" <cai@....us>
To:     "Thomas Gleixner" <tglx@...utronix.de>
Cc:     "linux kernel" <linux-kernel@...r.kernel.org>, arnd@...db.de,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Waiman Long" <longman@...hat.com>,
        "Yang Shi" <yang.shi@...ux.alibaba.com>
Subject: Re: [PATCH] debugobjects: add a new Kconfig for POOL_SIZE

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.
> 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.
> 
That’s a good point. I’ll send out a patch shortly.