L’ARC

	} else if (hdr->b_l1hdr.b_state == arc_mru) {
		/*
		 * This buffer has been accessed once recently and either
		 * its read is still in progress or it is in the cache.
		 */
		if (HDR_IO_IN_PROGRESS(hdr)) {
			hdr->b_l1hdr.b_arc_access = now;
			return;
		}
		hdr->b_l1hdr.b_mru_hits++;
		ARCSTAT_BUMP(arcstat_mru_hits);

		/*
		 * If the previous access was a prefetch, then it already
		 * handled possible promotion, so nothing more to do for now.
		 */
		if (was_prefetch) {
			hdr->b_l1hdr.b_arc_access = now;
			return;
		}

		/*
		 * If more than ARC_MINTIME have passed from the previous
		 * hit, promote the buffer to the MFU state.
		 */
		if (ddi_time_after(now, hdr->b_l1hdr.b_arc_access +
		    ARC_MINTIME)) {
			hdr->b_l1hdr.b_arc_access = now;
			DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, hdr);
			arc_change_state(arc_mfu, hdr);
		}

	if (hdr->b_l1hdr.b_pabd != NULL)
		arc_hdr_free_abd(hdr, B_FALSE);

	if (HDR_HAS_RABD(hdr))
		arc_hdr_free_abd(hdr, B_TRUE);

	arc_change_state(evicted_state, hdr);
	DTRACE_PROBE1(arc__evict, arc_buf_hdr_t *, hdr);
	if (evicted_state == arc_anon) {
		arc_hdr_destroy(hdr);
		*real_evicted += HDR_FULL_SIZE;
	} else {
		ASSERT(HDR_IN_HASH_TABLE(hdr));
	}

	return (bytes_evicted);

	/* Evict MRU metadata. */
	w = wt * (int64_t)(arc_meta * arc_pm >> 48) >> 16;
	e = MIN((int64_t)(asize - ac), (int64_t)(mrum - w));
	bytes = arc_evict_impl(arc_mru, ARC_BUFC_METADATA, e);
	total_evicted += bytes;
	mrum -= bytes;
	asize -= bytes;

	/* Evict MFU metadata. */
	w = wt * (int64_t)(arc_meta >> 16) >> 16;
	e = MIN((int64_t)(asize - ac), (int64_t)(m - bytes - w));
	bytes = arc_evict_impl(arc_mfu, ARC_BUFC_METADATA, e);
	total_evicted += bytes;
	mfum -= bytes;
	asize -= bytes;

	/* Evict MRU data. */
	wt -= m - total_evicted;
	w = wt * (int64_t)(arc_pd >> 16) >> 16;
	e = MIN((int64_t)(asize - ac), (int64_t)(mrud - w));
	bytes = arc_evict_impl(arc_mru, ARC_BUFC_DATA, e);
	total_evicted += bytes;
	mrud -= bytes;
	asize -= bytes;

	/* Evict MFU data. */
	e = asize - ac;
	bytes = arc_evict_impl(arc_mfu, ARC_BUFC_DATA, e);
	mfud -= bytes;
	total_evicted += bytes;

	/*
	 * Evict ghost lists
	 *
	 * Size of each state's ghost list represents how much that state
	 * may grow by shrinking the other states.  Would it need to shrink
	 * other states to zero (that is unlikely), its ghost size would be
	 * equal to sum of other three state sizes.  But excessive ghost
	 * size may result in false ghost hits (too far back), that may
	 * never result in real cache hits if several states are competing.
	 * So choose some arbitraty point of 1/2 of other state sizes.
	 */
	gsrd = (mrum + mfud + mfum) / 2;
	e = zfs_refcount_count(&arc_mru_ghost->arcs_size[ARC_BUFC_DATA]) -
	    gsrd;
	(void) arc_evict_impl(arc_mru_ghost, ARC_BUFC_DATA, e);

	gsrm = (mrud + mfud + mfum) / 2;
	e = zfs_refcount_count(&arc_mru_ghost->arcs_size[ARC_BUFC_METADATA]) -
	    gsrm;
	(void) arc_evict_impl(arc_mru_ghost, ARC_BUFC_METADATA, e);

	gsfd = (mrud + mrum + mfum) / 2;
	e = zfs_refcount_count(&arc_mfu_ghost->arcs_size[ARC_BUFC_DATA]) -
	    gsfd;
	(void) arc_evict_impl(arc_mfu_ghost, ARC_BUFC_DATA, e);

	gsfm = (mrud + mrum + mfud) / 2;
	e = zfs_refcount_count(&arc_mfu_ghost->arcs_size[ARC_BUFC_METADATA]) -
	    gsfm;
	(void) arc_evict_impl(arc_mfu_ghost, ARC_BUFC_METADATA, e);

	} else if (hdr->b_l1hdr.b_state == arc_mru_ghost) {
		arc_state_t	*new_state;
		/*
		 * This buffer has been accessed once recently, but was
		 * evicted from the cache.  Would we have bigger MRU, it
		 * would be an MRU hit, so handle it the same way, except
		 * we don't need to check the previous access time.
		 */
		hdr->b_l1hdr.b_mru_ghost_hits++;
		ARCSTAT_BUMP(arcstat_mru_ghost_hits);
		hdr->b_l1hdr.b_arc_access = now;
		wmsum_add(&arc_mru_ghost->arcs_hits[arc_buf_type(hdr)],
		    arc_hdr_size(hdr));
		if (was_prefetch) {
			new_state = arc_mru;
			DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, hdr);
		} else {
			new_state = arc_mfu;
			DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, hdr);
		}
		arc_change_state(new_state, hdr);

	/* Get ARC ghost hits since last eviction. */
	ngrd = wmsum_value(&arc_mru_ghost->arcs_hits[ARC_BUFC_DATA]);
	uint64_t grd = ngrd - ogrd;
	ogrd = ngrd;
	ngrm = wmsum_value(&arc_mru_ghost->arcs_hits[ARC_BUFC_METADATA]);
	uint64_t grm = ngrm - ogrm;
	ogrm = ngrm;
	ngfd = wmsum_value(&arc_mfu_ghost->arcs_hits[ARC_BUFC_DATA]);
	uint64_t gfd = ngfd - ogfd;
	ogfd = ngfd;
	ngfm = wmsum_value(&arc_mfu_ghost->arcs_hits[ARC_BUFC_METADATA]);
	uint64_t gfm = ngfm - ogfm;
	ogfm = ngfm;

	/* Adjust ARC states balance based on ghost hits. */
	arc_meta = arc_evict_adj(arc_meta, gsrd + gsrm + gsfd + gsfm,
	    grm + gfm, grd + gfd, zfs_arc_meta_balance);
	arc_pd = arc_evict_adj(arc_pd, gsrd + gsfd, grd, gfd, 100);
	arc_pm = arc_evict_adj(arc_pm, gsrm + gsfm, grm, gfm, 100);

static uint64_t
arc_evict_adj(uint64_t frac, uint64_t total, uint64_t up, uint64_t down,
    uint_t balance)
{
	if (total < 32 || up + down == 0)
		return (frac);

	/*
	 * We should not have more ghost hits than ghost size, but they may
	 * get close.  To avoid overflows below up/down should not be bigger
	 * than 1/5 of total.  But to limit maximum adjustment speed restrict
	 * it some more.
	 */
	if (up + down >= total / 16) {
		uint64_t scale = (up + down) / (total / 32);
		up /= scale;
		down /= scale;
	}

	/* Get maximal dynamic range by choosing optimal shifts. */
	int s = highbit64(total);
	s = MIN(64 - s, 32);

	ASSERT3U(frac, <=, 1ULL << 32);
	uint64_t ofrac = (1ULL << 32) - frac;

	if (frac >= 4 * ofrac)
		up /= frac / (2 * ofrac + 1);
	up = (up << s) / (total >> (32 - s));
	if (ofrac >= 4 * frac)
		down /= ofrac / (2 * frac + 1);
	down = (down << s) / (total >> (32 - s));
	down = down * 100 / balance;

	ASSERT3U(up, <=, (1ULL << 32) - frac);
	ASSERT3U(down, <=, frac);
	return (frac + up - down);
}