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SubjectRe: [PATCH v4] debugobjects: scale the static pool size
On Tue, 20 Nov 2018, Qian Cai wrote:

Looking deeper at that.

> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index 70935ed91125..140571aa483c 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -23,9 +23,81 @@
> #define ODEBUG_HASH_BITS 14
> #define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS)
>
> -#define ODEBUG_POOL_SIZE 1024
> +#define ODEBUG_DEFAULT_POOL 512
> #define ODEBUG_POOL_MIN_LEVEL 256
>
> +/*
> + * 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 (as today, 20 Nov. 2018),
> + *
> + * 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

None of the things are actually used or required _BEFORE_
debug_objects_mem_init() is invoked.

The reason why the call is at this place in start_kernel() is
historical. It's because back in the days when debugobjects were added the
memory allocator was enabled way later than today. So we can just move the
debug_objects_mem_init() call right before sched_init() I think.

> + * Increase the number a bit more in case the implmentatins are changed in the
> + * future, as it is better to avoid OOM than spending a bit more kernel memory
> + * that will/can be freed.
> + *
> + * With all debug objects config options selected except the workqueue and the
> + * timers, kernel reports,
> + * 64-CPU: ODEBUG: 4 of 4 active objects replaced
> + * 256-CPU: ODEBUG: 4 of 4 active objects replaced
> + *
> + * all the options except the workqueue:
> + * 64-CPU: ODEBUG: 466 of 466 active objects replaced
> + * 256-CPU: ODEBUG: 1810 of 1810 active objects replaced
> + *
> + * all the options except the timers:
> + * 64-CPU: ODEBUG: 652 of 652 active objects replaced
> + * 256-CPU: ODEBUG: 2572 of 2572 active objects replaced
> + *
> + * all the options:
> + * 64-CPU: ODEBUG: 1114 of 1114 active objects replaced
> + * 256-CPU: ODEBUG: 4378 of 4378 active objects replaced
> + */
> +#ifdef CONFIG_DEBUG_OBJECTS_WORK
> +#define ODEBUG_WORK_PCPU_CNT 10
> +#else
> +#define ODEBUG_WORK_PCPU_CNT 0
> +#endif /* CONFIG_DEBUG_OBJECTS_WORK */
> +
> +#ifdef CONFIG_DEBUG_OBJECTS_TIMERS
> +#define ODEBUG_TIMERS_PCPU_CNT 10
> +#else
> +#define ODEBUG_TIMERS_PCPU_CNT 0
> +#endif /* CONFIG_DEBUG_OBJECTS_TIMERS */

Btw, the scaling here is way off.

> +#define ODEBUG_POOL_SIZE (ODEBUG_DEFAULT_POOL + CONFIG_NR_CPUS * \
> + (ODEBUG_TIMERS_PCPU_CNT + ODEBUG_WORK_PCPU_CNT))

CONFIG_NR_CPUS Pool size Storage size

256 256512 4M

According to your list above it uses 4378 object for 256 CPUs. That's off
by an factor of ~58.

But we can spare all that and just move the init call.

Thanks,

tglx

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