linux-kernel - Re: [PATCH] debugobjects: scale the static pool size

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Message-ID: <f4c9756e-08c9-ce18-19a8-771977e95ac9@redhat.com>
Date:   Tue, 20 Nov 2018 08:50:52 -0500
From:   Waiman Long <longman@...hat.com>
To:     Qian Cai <cai@....us>, akpm@...ux-foundation.org,
        tglx@...utronix.de
Cc:     yang.shi@...ux.alibaba.com, arnd@...db.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugobjects: scale the static pool size

On 11/20/2018 01:42 AM, Qian Cai wrote:
> The current value of the early boot static pool size is not big enough
> for systems with large number of CPUs with timer or/and workqueue
> objects selected. As the results, systems have 60+ CPUs with both timer
> and workqueue objects enabled could trigger "ODEBUG: Out of memory.
> ODEBUG disabled". Hence, fixed it by computing it according to
> CONFIG_NR_CPUS and CONFIG_DEBUG_OBJECTS_* options.
>
> Signed-off-by: Qian Cai <cai@....us>
> ---
>  lib/debugobjects.c | 53 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index 70935ed91125..372dc34206d5 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -23,7 +23,53 @@
>  #define ODEBUG_HASH_BITS	14
>  #define ODEBUG_HASH_SIZE	(1 << ODEBUG_HASH_BITS)
>  
> +/*
> + * Some debug objects are allocated during the early boot. Enabling some
> + * options like timers or workqueue objects may increase the size required
> + * significantly with large number of CPUs. For example,
> + *
> + * No. CPUs x 2 (worker pool) objects:
> + *
> + * start_kernel
> + *   workqueue_init_early
> + *     init_worker_pool
> + *       init_timer_key
> + *         debug_object_init
> + *
> + * No. CPUs objects (CONFIG_HIGH_RES_TIMERS):
> + *
> + * sched_init
> + *   hrtick_rq_init
> + *     hrtimer_init
> + *
> + * CONFIG_DEBUG_OBJECTS_WORK:
> + * No. CPUs x 6 (workqueue) objects:
> + *
> + * workqueue_init_early
> + *   alloc_workqueue
> + *     __alloc_workqueue_key
> + *       alloc_and_link_pwqs
> + *         init_pwq
> + *
> + * Also, plus No. CPUs objects:
> + *
> + * perf_event_init
> + *    __init_srcu_struct
> + *      init_srcu_struct_fields
> + *        init_srcu_struct_nodes
> + *          __init_work
> + *
> + * Increase the number a bit more in case the implmentatins are changed in
> + * the future.
> + */
> +#if defined(CONFIG_NR_CPUS) && defined(CONFIG_DEBUG_OBJECTS_TIMERS) && \
> +!defined(CONFIG_DEBUG_OBJECTS_WORK)
> +#define ODEBUG_POOL_SIZE	(CONFIG_NR_CPUS * 10)
> +#elif defined(CONFIG_NR_CPUS) && defined(CONFIG_DEBUG_OBJECTS_WORK)
> +#define ODEBUG_POOL_SIZE	(CONFIG_NR_CPUS * 30)
> +#else
>  #define ODEBUG_POOL_SIZE	1024
> +#endif /* CONFIG_NR_CPUS */
>  #define ODEBUG_POOL_MIN_LEVEL	256
>  

CONFIG_NR_CPUS is always defined. You don't need to put that as a #if
condition. Where does the scaling factor 30 come from? It looks high to me.

For UP system, CONFIG_NR_CPUS will be 1. I think it is better to have a
guarantee minimum plus a multiplier of the # of configured CPUs.
Something like

512 + CONFIG_NR_CPUS * <multiplier>

where <multiplier> should be the sum of all early allocation objects
that scale with the number of cpus. The guarantee minimum will cover
other miscellaneous objects.

Cheers,
Longman