workqueue: The default node_nr_active should have its max set to max_…

…active

The default nna (node_nr_active) is used when the pool isn't tied to a
specific NUMA node. This can happen in the following cases:

 1. On NUMA, if per-node pwq init failure and the fallback pwq is used.
 2. On NUMA, if a pool is configured to span multiple nodes.
 3. On single node setups.

5797b1c ("workqueue: Implement system-wide nr_active enforcement for
unbound workqueues") set the default nna->max to min_active because only #1
was being considered. For #2 and #3, using min_active means that the max
concurrency in normal operation is pushed down to min_active which is
currently 8, which can obviously lead to performance issues.

exact value nna->max is set to doesn't really matter. #2 can only happen if
the workqueue is intentionally configured to ignore NUMA boundaries and
there's no good way to distribute max_active in this case. #3 is the default
behavior on single node machines.

Let's set it the default nna->max to max_active. This fixes the artificially
lowered concurrency problem on single node machines and shouldn't hurt
anything for other cases.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Fixes: 5797b1c ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues")
Link: https://lore.kernel.org/dm-devel/20240410084531.2134621-1-shinichiro.kawasaki@wdc.com/
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -1610,7 +1610,7 @@ static void wq_update_node_max_active(struct workqueue_struct *wq, int off_cpu)
 			      min_active, max_active);
 	}
 
-	wq_node_nr_active(wq, NUMA_NO_NODE)->max = min_active;
+	wq_node_nr_active(wq, NUMA_NO_NODE)->max = max_active;
 }
 
 /**