linux-kernel - Re: [PATCH v3] debugobjects: scale the static pool size

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Message-ID: <trinity-ce6c61be-cc03-4a9d-8f26-562694d048da-1542758061535@msvc-mesg-gmx023>
Date:   Wed, 21 Nov 2018 00:54:21 +0100
From:   "Qian Cai" <cai@....us>
To:     "Waiman Long" <longman@...hat.com>
Cc:     tglx@...utronix.de, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, yang.shi@...ux.alibaba.com,
        arnd@...db.de
Subject: Re: [PATCH v3] debugobjects: scale the static pool size

On 11/20/18 at 6:38 PM, Waiman Long wrote:

> On 11/20/2018 06:28 PM, 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>
> > ---
> > Changes since v2:
> > * Made the calculation easier to read suggested by longman@...hat.com.
> >
> > Changes since v1:
> > * Removed the CONFIG_NR_CPUS check since it is always defined.
> > * Introduced a minimal default pool size to start with. Otherwise, the pool
> >   size would be too low for systems only with a small number of CPUs.
> > * Adjusted the scale factors according to data.
> >
> >  lib/debugobjects.c | 82 ++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 80 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> > index 70935ed91125..02456a1e57cb 100644
> > --- a/lib/debugobjects.c
> > +++ b/lib/debugobjects.c
> > @@ -23,9 +23,82 @@
> >  #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
> > + *
> > + * 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 */
> > +
> > +#define ODEBUG_POOL_SIZE	(ODEBUG_DEFAULT_POOL + CONFIG_NR_CPUS * \
> > +(ODEBUG_TIMERS_PCPU_CNT + ODEBUG_WORK_PCPU_CNT))
> 
> Just a nit about indentation. There should be some indentation in the
> continued line.

I am fine to add that, but checkpatch.pl complained
that there should no spaces at the beginning of a
newline. Guess we just ignore the warning?

“please, no spaces at the start of a line”