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

Mathieu Desnoyers
2012-10-29T11:35:20Z

* Sasha Levin (levinsasha928@gmail.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@gmail.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.