// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/mm/swap_state.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 *
 *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
 */

/*
 * Official Linux v6.0: mm/swap_state.c
 * https://github.com/torvalds/linux/blob/v6.0/mm/swap_state.c#L325
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
			       unsigned long addr)
{
	struct page *page;
	struct swap_info_struct *si;

	si = get_swap_device(entry);
	if (!si)
		return NULL;
	page = find_get_page(swap_address_space(entry), swp_offset(entry));
	put_swap_device(si);

	if (page) {
		bool vma_ra = swap_use_vma_readahead();
		bool readahead;

		/*
		 * At the moment, we don't support PG_readahead for anon THP
		 * so let's bail out rather than confusing the readahead stat.
		 */
		if (unlikely(PageTransCompound(page)))
			return page;

		readahead = TestClearPageReadahead(page);
		if (vma && vma_ra) {
			unsigned long ra_val;
			int win, hits;

			ra_val = GET_SWAP_RA_VAL(vma);
			win = SWAP_RA_WIN(ra_val);
			hits = SWAP_RA_HITS(ra_val);
			if (readahead)
				hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
			atomic_long_set(&vma->swap_readahead_info,
					SWAP_RA_VAL(addr, win, hits));
		}

		if (readahead) {
			count_vm_event(SWAP_RA_HIT);
			if (!vma || !vma_ra)
				atomic_inc(&swapin_readahead_hits);
		}
	}

	return page;
}