On 2024/9/10 2:41, Thomas Gleixner wrote:
> On Wed, Sep 04 2024 at 21:41, Zhen Lei wrote:
>
>> Currently, there are multiple instances where several nodes are extracted
>> from one list and added to another list. One by one extraction, and then
>> one by one splicing, not only low efficiency, readability is also poor.
>> The work can be done well with hlist_cut_number() and hlist_splice_init(),
>> which move the entire sublist at once.
>>
>> When the number of nodes expected to be moved is less than or equal to 0,
>> or the source list is empty, hlist_cut_number() safely returns 0. The
>> splicing is performed only when the return value of hlist_cut_number() is
>> greater than 0.
>>
>> For two calls to hlist_cut_number() in __free_object(), the result is
>> obviously positive, the check of the return value is omitted.
>
> Sure but hlist_cut_number() suffers from the same problem as the current
> code. If is a massive cache line chase as you actually have to walk the
> list to figure out where to cut it off.
>
> All related functions have this problem and all of this code is very
> strict about boundaries. Instead of accurately doing the refill, purge
> etc. we should look into proper batch mode mechanisms. Let me think
> about it.
It may be helpful to add several arrays to record the first node of each batch
in each free list. Take 'percpu_pool' as an example:
struct debug_percpu_free {
struct hlist_head free_objs;
int obj_free;
+ int batch_idx;
+ struct hlist_node *batch_first[4]; // ODEBUG_POOL_PERCPU_SIZE / ODEBUG_BATCH_SIZE
};
A new free node is added to the header of the list, and the batch is cut from the tail
of the list.
NodeA<-->...<-->NodeB<-->...<-->NodeC<-->NodeD<--> free_objs
|---one batch---|---one batch---|
| |
batch_first[0] batch_first[1]
__free_object():
//add obj into percpu_pool
obj_free++;
if (obj_free % ODEBUG_BATCH_SIZE == 0) {
idx = 0x3 & (batch_idx + (obj_free / ODEBUG_BATCH_SIZE) - 1);
//update batch_first[idx]
}
if (obj_free >= ODEBUG_POOL_PERCPU_SIZE) {
//move one batch
//cut batch at 'batch_idx' into obj_to_free (or obj_pool, if less than debug_objects_pool_min_level)
batch_idx++;
obj_free -= ODEBUG_BATCH_SIZE
}
>
> Thanks,
>
> tglx
>
>
> .
>
--
Regards,
Zhen Lei
