Recently the separate worker thread has been introduced to maintain the local page cache from the regular kernel context, instead of kvfree_rcu() contexts. That was done because a caller of the k[v]free_rcu() can be any context type what is a problem from the allocation point of view.
>From the other hand, the lock-less way of obtaining a page has been introduced and directly injected to the k[v]free_rcu() path. Therefore it is not important anymore to use a high priority "wq" for the external job that used to fill a page cache ASAP when it was empty. Signed-off-by: Uladzislau Rezki (Sony) <[email protected]> --- kernel/rcu/tree.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d51209343029..f2b4215631f7 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3100,7 +3100,7 @@ struct kfree_rcu_cpu { * lockless an access has to be protected by the * per-cpu lock. */ - struct work_struct page_cache_work; + struct delayed_work page_cache_work; atomic_t work_in_progress; struct llist_head bkvcache; int nr_bkv_objs; @@ -3354,7 +3354,7 @@ static void fill_page_cache_func(struct work_struct *work) struct kvfree_rcu_bulk_data *bnode; struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, - page_cache_work); + page_cache_work.work); unsigned long flags; bool pushed; int i; @@ -3440,7 +3440,6 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) { unsigned long flags; struct kfree_rcu_cpu *krcp; - bool irq_disabled = irqs_disabled(); bool success; void *ptr; @@ -3473,9 +3472,9 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr); if (!success) { - // TODO: schedule the work from the hrtimer. - if (!irq_disabled && !atomic_xchg(&krcp->work_in_progress, 1)) - queue_work(system_highpri_wq, &krcp->page_cache_work); + // Use delayed work, so we do not deadlock with rq->lock. + if (!atomic_xchg(&krcp->work_in_progress, 1)) + schedule_delayed_work(&krcp->page_cache_work, 1); if (head == NULL) // Inline if kvfree_rcu(one_arg) call. @@ -4475,7 +4474,7 @@ static void __init kfree_rcu_batch_init(void) } INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor); - INIT_WORK(&krcp->page_cache_work, fill_page_cache_func); + INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func); krcp->initialized = true; } if (register_shrinker(&kfree_rcu_shrinker)) -- 2.20.1
