// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/swapfile.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 */

/*
 * Official Linux v6.18: mm/swapfile.c
 * https://github.com/torvalds/linux/blob/v6.18/mm/swapfile.c#L1408
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

int folio_alloc_swap(struct folio *folio, gfp_t gfp)
{
	unsigned int order = folio_order(folio);
	unsigned int size = 1 << order;
	swp_entry_t entry = {};

	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
	VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);

	if (order) {
		/*
		 * Reject large allocation when THP_SWAP is disabled,
		 * the caller should split the folio and try again.
		 */
		if (!IS_ENABLED(CONFIG_THP_SWAP))
			return -EAGAIN;

		/*
		 * Allocation size should never exceed cluster size
		 * (HPAGE_PMD_SIZE).
		 */
		if (size > SWAPFILE_CLUSTER) {
			VM_WARN_ON_ONCE(1);
			return -EINVAL;
		}
	}

	local_lock(&percpu_swap_cluster.lock);
	if (!swap_alloc_fast(&entry, order))
		swap_alloc_slow(&entry, order);
	local_unlock(&percpu_swap_cluster.lock);

	/* Need to call this even if allocation failed, for MEMCG_SWAP_FAIL. */
	if (mem_cgroup_try_charge_swap(folio, entry))
		goto out_free;

	if (!entry.val)
		return -ENOMEM;

	swap_cache_add_folio(folio, entry, NULL);

	return 0;

out_free:
	put_swap_folio(folio, entry);
	return -ENOMEM;
}