Re: [PATCH RFC v4 1/3] block: add BIO_COMPLETE_IN_TASK for task-context completion

[Matthew Wilcox <willy@infradead.org>]

On Wed, Mar 25, 2026 at 02:43:00PM -0400, Tal Zussman wrote:
> +static void bio_complete_work_fn(struct work_struct *w)
> +{
> +	struct bio_complete_batch *batch;
> +	struct bio_list list;
> +
> +again:
> +	local_lock_irq(&bio_complete_batch.lock);
> +	batch = this_cpu_ptr(&bio_complete_batch);
> +	list = batch->list;
> +	bio_list_init(&batch->list);
> +	local_unlock_irq(&bio_complete_batch.lock);
> +
> +	while (!bio_list_empty(&list)) {
> +		struct bio *bio = bio_list_pop(&list);
> +		bio->bi_end_io(bio);
> +	}
> +
> +	local_lock_irq(&bio_complete_batch.lock);
> +	batch = this_cpu_ptr(&bio_complete_batch);
> +	if (!bio_list_empty(&batch->list)) {
> +		local_unlock_irq(&bio_complete_batch.lock);
> +
> +		if (!need_resched())
> +			goto again;
> +
> +		schedule_work_on(smp_processor_id(), &batch->work);
> +		return;
> +	}

I don't know how often we see this actually trigger, but wouldn't this
be slightly more efficient?

+	local_lock_irq(&bio_complete_batch.lock);
+	batch = this_cpu_ptr(&bio_complete_batch);
+	list = batch->list;
+again:
+	bio_list_init(&batch->list);
+	local_unlock_irq(&bio_complete_batch.lock);
+
+	while (!bio_list_empty(&list)) {
+		struct bio *bio = bio_list_pop(&list);
+		bio->bi_end_io(bio);
+	}
+
+	local_lock_irq(&bio_complete_batch.lock);
+	batch = this_cpu_ptr(&bio_complete_batch);
+	list = batch->list;
+	if (!bio_list_empty(&list)) {
+		if (!need_resched())
+			goto again;
+
+		local_unlock_irq(&bio_complete_batch.lock);
+		schedule_work_on(smp_processor_id(), &batch->work);
+		return;
+	}


Overall I like this.  I think this is a better approach than the earlier
patches, and I'm looking forward to the simplifications that it's going
to enable.