// 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 v6.12, mm/vmscan.c:5857-5934.
 * Full function definition; surrounding kernel context is required.
 * Source: https://github.com/torvalds/linux/blob/v6.12/mm/vmscan.c#L5857
 * License text: GPL-2.0.txt (in this directory).
 */
static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
{
	struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
	struct mem_cgroup_reclaim_cookie reclaim = {
		.pgdat = pgdat,
	};
	struct mem_cgroup_reclaim_cookie *partial = &reclaim;
	struct mem_cgroup *memcg;

	/*
	 * In most cases, direct reclaimers can do partial walks
	 * through the cgroup tree, using an iterator state that
	 * persists across invocations. This strikes a balance between
	 * fairness and allocation latency.
	 *
	 * For kswapd, reliable forward progress is more important
	 * than a quick return to idle. Always do full walks.
	 */
	if (current_is_kswapd() || sc->memcg_full_walk)
		partial = NULL;

	memcg = mem_cgroup_iter(target_memcg, NULL, partial);
	do {
		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
		unsigned long reclaimed;
		unsigned long scanned;

		/*
		 * This loop can become CPU-bound when target memcgs
		 * aren't eligible for reclaim - either because they
		 * don't have any reclaimable pages, or because their
		 * memory is explicitly protected. Avoid soft lockups.
		 */
		cond_resched();

		mem_cgroup_calculate_protection(target_memcg, memcg);

		if (mem_cgroup_below_min(target_memcg, memcg)) {
			/*
			 * Hard protection.
			 * If there is no reclaimable memory, OOM.
			 */
			continue;
		} else if (mem_cgroup_below_low(target_memcg, memcg)) {
			/*
			 * Soft protection.
			 * Respect the protection only as long as
			 * there is an unprotected supply
			 * of reclaimable memory from other cgroups.
			 */
			if (!sc->memcg_low_reclaim) {
				sc->memcg_low_skipped = 1;
				continue;
			}
			memcg_memory_event(memcg, MEMCG_LOW);
		}

		reclaimed = sc->nr_reclaimed;
		scanned = sc->nr_scanned;

		shrink_lruvec(lruvec, sc);

		shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
			    sc->priority);

		/* Record the group's reclaim efficiency */
		if (!sc->proactive)
			vmpressure(sc->gfp_mask, memcg, false,
				   sc->nr_scanned - scanned,
				   sc->nr_reclaimed - reclaimed);

		/* If partial walks are allowed, bail once goal is reached */
		if (partial && sc->nr_reclaimed >= sc->nr_to_reclaim) {
			mem_cgroup_iter_break(target_memcg, memcg);
			break;
		}
	} while ((memcg = mem_cgroup_iter(target_memcg, memcg, partial)));
}