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    SubjectRe: [PATCH v7 06/16] tracepoint: use new hashtable implementation
    On Mon, Oct 29, 2012 at 7:35 AM, Mathieu Desnoyers
    <mathieu.desnoyers@efficios.com> wrote:
    > * 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).

    This was discussed in the previous series, the conclusion was to call
    hash_init() either way to keep the encapsulation and consistency.

    It's cheap enough and happens only once, so why not?


    Thanks,
    Sasha


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