linux-kernel - Re: [PATCH v7 06/16] tracepoint: use new hashtable implementation

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Message-ID: <20121029113515.GB9115@Krystal>
Date:	Mon, 29 Oct 2012 07:35:15 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v7 06/16] tracepoint: use new hashtable implementation

* Sasha Levin (levinsasha928@...il.com) wrote:
> Switch tracepoints to use the new hashtable implementation. This reduces the amount of
> generic unrelated code in the tracepoints.
> 
> Signed-off-by: Sasha Levin <levinsasha928@...il.com>
> ---
>  kernel/tracepoint.c | 27 +++++++++++----------------
>  1 file changed, 11 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index d96ba22..854df92 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -26,6 +26,7 @@
>  #include <linux/slab.h>
>  #include <linux/sched.h>
>  #include <linux/static_key.h>
> +#include <linux/hashtable.h>
>  
>  extern struct tracepoint * const __start___tracepoints_ptrs[];
>  extern struct tracepoint * const __stop___tracepoints_ptrs[];
> @@ -49,8 +50,7 @@ static LIST_HEAD(tracepoint_module_list);
>   * Protected by tracepoints_mutex.
>   */
>  #define TRACEPOINT_HASH_BITS 6
> -#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
> -static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
> +static DEFINE_HASHTABLE(tracepoint_table, TRACEPOINT_HASH_BITS);
>  
[...]
>  
> @@ -722,6 +715,8 @@ struct notifier_block tracepoint_module_nb = {
>  
>  static int init_tracepoints(void)
>  {
> +	hash_init(tracepoint_table);
> +
>  	return register_module_notifier(&tracepoint_module_nb);
>  }
>  __initcall(init_tracepoints);

So we have a hash table defined in .bss (therefore entirely initialized
to NULL), and you add a call to "hash_init", which iterates on the whole
array and initialize it to NULL (again) ?

This extra initialization is redundant. I think it should be removed
from here, and hashtable.h should document that hash_init() don't need
to be called on zeroed memory (which includes static/global variables,
kzalloc'd memory, etc).

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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