// 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:540-607.
 * Complete function definition; surrounding kernel context is required.
 * Source: https://github.com/torvalds/linux/blob/v6.18/mm/vmscan.c#L540
 * License text: GPL-2.0.txt (in this directory).
 */
void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
{
	wait_queue_head_t *wqh = &pgdat->reclaim_wait[reason];
	long timeout, ret;
	DEFINE_WAIT(wait);

	/*
	 * Do not throttle user workers, kthreads other than kswapd or
	 * workqueues. They may be required for reclaim to make
	 * forward progress (e.g. journalling workqueues or kthreads).
	 */
	if (!current_is_kswapd() &&
	    current->flags & (PF_USER_WORKER|PF_KTHREAD)) {
		cond_resched();
		return;
	}

	/*
	 * These figures are pulled out of thin air.
	 * VMSCAN_THROTTLE_ISOLATED is a transient condition based on too many
	 * parallel reclaimers which is a short-lived event so the timeout is
	 * short. Failing to make progress or waiting on writeback are
	 * potentially long-lived events so use a longer timeout. This is shaky
	 * logic as a failure to make progress could be due to anything from
	 * writeback to a slow device to excessive referenced folios at the tail
	 * of the inactive LRU.
	 */
	switch(reason) {
	case VMSCAN_THROTTLE_WRITEBACK:
		timeout = HZ/10;

		if (atomic_inc_return(&pgdat->nr_writeback_throttled) == 1) {
			WRITE_ONCE(pgdat->nr_reclaim_start,
				node_page_state(pgdat, NR_THROTTLED_WRITTEN));
		}

		break;
	case VMSCAN_THROTTLE_CONGESTED:
		fallthrough;
	case VMSCAN_THROTTLE_NOPROGRESS:
		if (skip_throttle_noprogress(pgdat)) {
			cond_resched();
			return;
		}

		timeout = 1;

		break;
	case VMSCAN_THROTTLE_ISOLATED:
		timeout = HZ/50;
		break;
	default:
		WARN_ON_ONCE(1);
		timeout = HZ;
		break;
	}

	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
	ret = schedule_timeout(timeout);
	finish_wait(wqh, &wait);

	if (reason == VMSCAN_THROTTLE_WRITEBACK)
		atomic_dec(&pgdat->nr_writeback_throttled);

	trace_mm_vmscan_throttled(pgdat->node_id, jiffies_to_usecs(timeout),
				jiffies_to_usecs(timeout - ret),
				reason);
}