debugobjects: Implement batch processing

Adding and removing single objects in a loop is bad in terms of lock
contention and cache line accesses.

To implement batching, record the last object in a batch in the object
itself. This is trivialy possible as hlists are strictly stacks. At a batch
boundary, when the first object is added to the list the object stores a
pointer to itself in debug_obj::batch_last. When the next object is added
to the list then the batch_last pointer is retrieved from the first object
in the list and stored in the to be added one.

That means for batch processing the first object always has a pointer to
the last object in a batch, which allows to move batches in a cache line
efficient way and reduces the lock held time.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/all/20241007164914.258995000@linutronix.de

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index cdd5d23..4e80c31 100644 (file)
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -149,18 +149,31 @@ static __always_inline bool pool_must_refill(struct obj_pool *pool)
 
 static bool pool_move_batch(struct obj_pool *dst, struct obj_pool *src)
 {
-       if (dst->cnt + ODEBUG_BATCH_SIZE > dst->max_cnt || !src->cnt)
+       struct hlist_node *last, *next_batch, *first_batch;
+       struct debug_obj *obj;
+
+       if (dst->cnt >= dst->max_cnt || !src->cnt)
                return false;
 
-       for (int i = 0; i < ODEBUG_BATCH_SIZE && src->cnt; i++) {
-               struct hlist_node *node = src->objects.first;
+       first_batch = src->objects.first;
+       obj = hlist_entry(first_batch, typeof(*obj), node);
+       last = obj->batch_last;
+       next_batch = last->next;
 
-               WRITE_ONCE(src->cnt, src->cnt - 1);
-               WRITE_ONCE(dst->cnt, dst->cnt + 1);
+       /* Move the next batch to the front of the source pool */
+       src->objects.first = next_batch;
+       if (next_batch)
+               next_batch->pprev = &src->objects.first;
 
-               hlist_del(node);
-               hlist_add_head(node, &dst->objects);
-       }
+       /* Add the extracted batch to the destination pool */
+       last->next = dst->objects.first;
+       if (last->next)
+               last->next->pprev = &last->next;
+       first_batch->pprev = &dst->objects.first;
+       dst->objects.first = first_batch;
+
+       WRITE_ONCE(src->cnt, src->cnt - ODEBUG_BATCH_SIZE);
+       WRITE_ONCE(dst->cnt, dst->cnt + ODEBUG_BATCH_SIZE);
        return true;
 }
 
@@ -182,16 +195,27 @@ static bool pool_push_batch(struct obj_pool *dst, struct hlist_head *head)
 
 static bool pool_pop_batch(struct hlist_head *head, struct obj_pool *src)
 {
+       struct hlist_node *last, *next;
+       struct debug_obj *obj;
+
        if (!src->cnt)
                return false;
 
-       for (int i = 0; src->cnt && i < ODEBUG_BATCH_SIZE; i++) {
-               struct hlist_node *node = src->objects.first;
+       /* Move the complete list to the head */
+       hlist_move_list(&src->objects, head);
 
-               WRITE_ONCE(src->cnt, src->cnt - 1);
-               hlist_del(node);
-               hlist_add_head(node, head);
-       }
+       obj = hlist_entry(head->first, typeof(*obj), node);
+       last = obj->batch_last;
+       next = last->next;
+       /* Disconnect the batch from the list */
+       last->next = NULL;
+
+       /* Move the node after last back to the source pool. */
+       src->objects.first = next;
+       if (next)
+               next->pprev = &src->objects.first;
+
+       WRITE_ONCE(src->cnt, src->cnt - ODEBUG_BATCH_SIZE);
        return true;
 }
 
@@ -226,7 +250,7 @@ static struct debug_obj *pcpu_alloc(void)
                        if (!pool_move_batch(pcp, &pool_global))
                                return NULL;
                }
-               obj_pool_used += pcp->cnt;
+               obj_pool_used += ODEBUG_BATCH_SIZE;
 
                if (obj_pool_used > obj_pool_max_used)
                        obj_pool_max_used = obj_pool_used;
@@ -239,9 +263,16 @@ static struct debug_obj *pcpu_alloc(void)
 static void pcpu_free(struct debug_obj *obj)
 {
        struct obj_pool *pcp = this_cpu_ptr(&pool_pcpu);
+       struct debug_obj *first;
 
        lockdep_assert_irqs_disabled();
 
+       if (!(pcp->cnt % ODEBUG_BATCH_SIZE)) {
+               obj->batch_last = &obj->node;
+       } else {
+               first = hlist_entry(pcp->objects.first, typeof(*first), node);
+               obj->batch_last = first->batch_last;
+       }
        hlist_add_head(&obj->node, &pcp->objects);
        pcp->cnt++;