// 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 v6.0, mm/vmscan.c:1215-1283.
 * Complete function definition; surrounding kernel context is required.
 * Source: https://github.com/torvalds/linux/blob/v6.0/mm/vmscan.c#L1215
 * License text: GPL-2.0.txt (in this directory).
 */
static pageout_t pageout(struct folio *folio, struct address_space *mapping,
			 struct swap_iocb **plug)
{
	/*
	 * If the folio is dirty, only perform writeback if that write
	 * will be non-blocking.  To prevent this allocation from being
	 * stalled by pagecache activity.  But note that there may be
	 * stalls if we need to run get_block().  We could test
	 * PagePrivate for that.
	 *
	 * If this process is currently in __generic_file_write_iter() against
	 * this folio's queue, we can perform writeback even if that
	 * will block.
	 *
	 * If the folio is swapcache, write it back even if that would
	 * block, for some throttling. This happens by accident, because
	 * swap_backing_dev_info is bust: it doesn't reflect the
	 * congestion state of the swapdevs.  Easy to fix, if needed.
	 */
	if (!is_page_cache_freeable(folio))
		return PAGE_KEEP;
	if (!mapping) {
		/*
		 * Some data journaling orphaned folios can have
		 * folio->mapping == NULL while being dirty with clean buffers.
		 */
		if (folio_test_private(folio)) {
			if (try_to_free_buffers(folio)) {
				folio_clear_dirty(folio);
				pr_info("%s: orphaned folio\n", __func__);
				return PAGE_CLEAN;
			}
		}
		return PAGE_KEEP;
	}
	if (mapping->a_ops->writepage == NULL)
		return PAGE_ACTIVATE;

	if (folio_clear_dirty_for_io(folio)) {
		int res;
		struct writeback_control wbc = {
			.sync_mode = WB_SYNC_NONE,
			.nr_to_write = SWAP_CLUSTER_MAX,
			.range_start = 0,
			.range_end = LLONG_MAX,
			.for_reclaim = 1,
			.swap_plug = plug,
		};

		folio_set_reclaim(folio);
		res = mapping->a_ops->writepage(&folio->page, &wbc);
		if (res < 0)
			handle_write_error(mapping, folio, res);
		if (res == AOP_WRITEPAGE_ACTIVATE) {
			folio_clear_reclaim(folio);
			return PAGE_ACTIVATE;
		}

		if (!folio_test_writeback(folio)) {
			/* synchronous write or broken a_ops? */
			folio_clear_reclaim(folio);
		}
		trace_mm_vmscan_write_folio(folio);
		node_stat_add_folio(folio, NR_VMSCAN_WRITE);
		return PAGE_SUCCESS;
	}

	return PAGE_CLEAN;
}