static int virtballoon_migratepage()

in virtio_balloon.c [753:807]

• 32 lines of code
• 4 McCabe index (conditional complexity)

static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
		struct page *newpage, struct page *page, enum migrate_mode mode)
{
	struct virtio_balloon *vb = container_of(vb_dev_info,
			struct virtio_balloon, vb_dev_info);
	unsigned long flags;

	/*
	 * In order to avoid lock contention while migrating pages concurrently
	 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
	 * this turn, as it is easier to retry the page migration later.
	 * This also prevents fill_balloon() getting stuck into a mutex
	 * recursion in the case it ends up triggering memory compaction
	 * while it is attempting to inflate the ballon.
	 */
	if (!mutex_trylock(&vb->balloon_lock))
		return -EAGAIN;

	get_page(newpage); /* balloon reference */

	/*
	  * When we migrate a page to a different zone and adjusted the
	  * managed page count when inflating, we have to fixup the count of
	  * both involved zones.
	  */
	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM) &&
	    page_zone(page) != page_zone(newpage)) {
		adjust_managed_page_count(page, 1);
		adjust_managed_page_count(newpage, -1);
	}

	/* balloon's page migration 1st step  -- inflate "newpage" */
	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
	balloon_page_insert(vb_dev_info, newpage);
	vb_dev_info->isolated_pages--;
	__count_vm_event(BALLOON_MIGRATE);
	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
	set_page_pfns(vb, vb->pfns, newpage);
	tell_host(vb, vb->inflate_vq);

	/* balloon's page migration 2nd step -- deflate "page" */
	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
	balloon_page_delete(page);
	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
	set_page_pfns(vb, vb->pfns, page);
	tell_host(vb, vb->deflate_vq);

	mutex_unlock(&vb->balloon_lock);

	put_page(page); /* balloon reference */

	return MIGRATEPAGE_SUCCESS;
}