On 2013/1/9 2:17, Tejun Heo wrote:
> Hello, Li.
>
> On Tue, Jan 08, 2013 at 03:51:45PM +0800, Li Zefan wrote:
>> -static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
>> +static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
>> {
>> int i;
>> - int index;
>> - unsigned long tmp = 0UL;
>> + unsigned long key = 0UL;
>>
>> for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
>> - tmp += (unsigned long)css[i];
>> - tmp = (tmp >> 16) ^ tmp;
>> + key += (unsigned long)css[i];
>> + key = (key >> 16) ^ key;
>
> @key is gonna go through hash function anyway. Do we still need the
> above (key >> 16) ^ key? It's not gonna help anything.
>
Nothing's changed after this patch, so the key will still be passed to
hash_long().
I tested this hash function long ago, and the original version was
without (key >> 16) ^ key, and it produced worse hash collision.
>> - index = hash_long(tmp, CSS_SET_HASH_BITS);
>> -
>> - return &css_set_table[index];
>> + return key;
>> }
>>
>> /* We don't maintain the lists running through each css_set to its
>> @@ -4503,23 +4498,17 @@ int __init_or_module cgroup_load_subsys(struct
>> cgroup_subsys *ss)
>> * this is all done under the css_set_lock.
>> */
>> write_lock(&css_set_lock);
>> - for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
>> - struct css_set *cg;
>> - struct hlist_node *node, *tmp;
>> - struct hlist_head *bucket = &css_set_table[i], *new_bucket;
>> -
>> - hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) {
>> - /* skip entries that we already rehashed */
>> - if (cg->subsys[ss->subsys_id])
>> - continue;
>> - /* remove existing entry */
>> - hlist_del(&cg->hlist);
>> - /* set new value */
>> - cg->subsys[ss->subsys_id] = css;
>> - /* recompute hash and restore entry */
>> - new_bucket = css_set_hash(cg->subsys);
>> - hlist_add_head(&cg->hlist, new_bucket);
>> - }
>> + hash_for_each_safe(css_set_table, i, node, tmp, cg, hlist) {
>> + /* skip entries that we already rehashed */
>> + if (cg->subsys[ss->subsys_id])
>> + continue;
>> + /* remove existing entry */
>> + hlist_del(&cg->hlist);
>
> hash_del()?
>
will fix.
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