// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, Stephen Tweedie.
 *  kswapd added: 7.1.96  sct
 *  Removed kswapd_ctl limits, and swap out as many pages as needed
 *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
 *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
 *  Multiqueue VM started 5.8.00, Rik van Riel.
 */

/* Extracted unchanged from Linux v6.18, mm/vmscan.c:2556-2670.
 * Full function definition; surrounding kernel context is required.
 * Source: https://github.com/torvalds/linux/blob/v6.18/mm/vmscan.c#L2556
 * License text: GPL-2.0.txt (in this directory).
 */
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
			   unsigned long *nr)
{
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
	int swappiness = sc_swappiness(sc, memcg);
	u64 fraction[ANON_AND_FILE];
	u64 denominator = 0;	/* gcc */
	enum scan_balance scan_balance;
	enum lru_list lru;

	/* If we have no swap space, do not bother scanning anon folios. */
	if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	/*
	 * Global reclaim will swap to prevent OOM even with no
	 * swappiness, but memcg users want to use this knob to
	 * disable swapping for individual groups completely when
	 * using the memory controller's swap limit feature would be
	 * too expensive.
	 */
	if (cgroup_reclaim(sc) && !swappiness) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	/* Proactive reclaim initiated by userspace for anonymous memory only */
	if (swappiness == SWAPPINESS_ANON_ONLY) {
		WARN_ON_ONCE(!sc->proactive);
		scan_balance = SCAN_ANON;
		goto out;
	}

	/*
	 * Do not apply any pressure balancing cleverness when the
	 * system is close to OOM, scan both anon and file equally
	 * (unless the swappiness setting disagrees with swapping).
	 */
	if (!sc->priority && swappiness) {
		scan_balance = SCAN_EQUAL;
		goto out;
	}

	/*
	 * If the system is almost out of file pages, force-scan anon.
	 */
	if (sc->file_is_tiny) {
		scan_balance = SCAN_ANON;
		goto out;
	}

	/*
	 * If there is enough inactive page cache, we do not reclaim
	 * anything from the anonymous working right now to make sure
         * a streaming file access pattern doesn't cause swapping.
	 */
	if (sc->cache_trim_mode) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	scan_balance = SCAN_FRACT;
	calculate_pressure_balance(sc, swappiness, fraction, &denominator);

out:
	for_each_evictable_lru(lru) {
		bool file = is_file_lru(lru);
		unsigned long lruvec_size;
		unsigned long scan;

		lruvec_size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
		scan = apply_proportional_protection(memcg, sc, lruvec_size);
		scan >>= sc->priority;

		/*
		 * If the cgroup's already been deleted, make sure to
		 * scrape out the remaining cache.
		 */
		if (!scan && !mem_cgroup_online(memcg))
			scan = min(lruvec_size, SWAP_CLUSTER_MAX);

		switch (scan_balance) {
		case SCAN_EQUAL:
			/* Scan lists relative to size */
			break;
		case SCAN_FRACT:
			/*
			 * Scan types proportional to swappiness and
			 * their relative recent reclaim efficiency.
			 * Make sure we don't miss the last page on
			 * the offlined memory cgroups because of a
			 * round-off error.
			 */
			scan = mem_cgroup_online(memcg) ?
			       div64_u64(scan * fraction[file], denominator) :
			       DIV64_U64_ROUND_UP(scan * fraction[file],
						  denominator);
			break;
		case SCAN_FILE:
		case SCAN_ANON:
			/* Scan one type exclusively */
			if ((scan_balance == SCAN_FILE) != file)
				scan = 0;
			break;
		default:
			/* Look ma, no brain */
			BUG();
		}

		nr[lru] = scan;
	}
}