Function l2arc_write_buffers

freebsd/contrib/openzfs/module/zfs/arc.c:9058–9324

* Find and write ARC buffers to the L2ARC device. * * An ARC_FLAG_L2_WRITING flag is set so that the L2ARC buffers are not valid * for reading until they have completed writing. * The headroom_boost is an in-out parameter used to maintain headroom boost * state between calls to this function. * * Returns the number of bytes actually written (which may be smaller than * the delta by which t

 * writing of log blocks).
 */
static uint64_t
l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz)
{
	arc_buf_hdr_t 		*hdr, *hdr_prev, *head;
	uint64_t 		write_asize, write_psize, write_lsize, headroom;
	boolean_t		full;
	l2arc_write_callback_t	*cb = NULL;
	zio_t 			*pio, *wzio;
	uint64_t 		guid = spa_load_guid(spa);
	l2arc_dev_hdr_phys_t	*l2dhdr = dev->l2ad_dev_hdr;

	ASSERT3P(dev->l2ad_vdev, !=, NULL);

	pio = NULL;
	write_lsize = write_asize = write_psize = 0;
	full = B_FALSE;
	head = kmem_cache_alloc(hdr_l2only_cache, KM_PUSHPAGE);
	arc_hdr_set_flags(head, ARC_FLAG_L2_WRITE_HEAD | ARC_FLAG_HAS_L2HDR);

	/*
	 * Copy buffers for L2ARC writing.
	 */
	for (int try = 0; try < L2ARC_FEED_TYPES; try++) {
		/*
		 * If try == 1 or 3, we cache MRU metadata and data
		 * respectively.
		 */
		if (l2arc_mfuonly) {
			if (try == 1 || try == 3)
				continue;
		}

		multilist_sublist_t *mls = l2arc_sublist_lock(try);
		uint64_t passed_sz = 0;

		VERIFY3P(mls, !=, NULL);

		/*
		 * L2ARC fast warmup.
		 *
		 * Until the ARC is warm and starts to evict, read from the
		 * head of the ARC lists rather than the tail.
		 */
		if (arc_warm == B_FALSE)
			hdr = multilist_sublist_head(mls);
		else
			hdr = multilist_sublist_tail(mls);

		headroom = target_sz * l2arc_headroom;
		if (zfs_compressed_arc_enabled)
			headroom = (headroom * l2arc_headroom_boost) / 100;

		for (; hdr; hdr = hdr_prev) {
			kmutex_t *hash_lock;
			abd_t *to_write = NULL;

			if (arc_warm == B_FALSE)
				hdr_prev = multilist_sublist_next(mls, hdr);