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

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Date:   Sun, 18 Nov 2018 19:21:24 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Qian Cai <cai@....us>
cc:     akpm@...ux-foundation.org, longman@...hat.com,
        yang.shi@...ux.alibaba.com, arnd@...db.de,
        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:

> The current value of ODEBUG_POOL_SIZE is not big enough for large memory
> systems with timer or/and workqueue objects because during the early
> boot, timer objects needs at least the size equals to
> 
> No. CPUs x 2 (worker pool)
> 
> start_kernel
>   workqueue_init_early
>     init_worker_pool
>       init_timer_key
>         debug_object_init
> 
> puls, No. CPUs
> 
> start_kernel
>   sched_init
>     hrtimer_init
>      debug_object_init
> 
> Then, workqueue objects requires even more,
> 
> No. CPUs x 2 (worker pool) x 6 (workqueue)
> 
> start_kernel
>   workqueue_init_early
>     __alloc_workqueue_key
>       alloc_workqueue
>         init_pwq
>           debug_object_init
> 
> plus, No, CPUs x 2 (worker pool)
> 
> start_kernel
>   perf_event_init
>     __init_srcu_struct
>       init_srcu_struct_fields
>         __init_work
>           debug_object_init
> 
> 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?

Thanks,

	tglx