// 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 v6.12: mm/swap_state.c
 * https://github.com/torvalds/linux/blob/v6.12/mm/swap_state.c#L799
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
		struct mempolicy *mpol, pgoff_t targ_ilx, struct vm_fault *vmf)
{
	struct blk_plug plug;
	struct swap_iocb *splug = NULL;
	struct folio *folio;
	pte_t *pte = NULL, pentry;
	int win;
	unsigned long start, end, addr;
	swp_entry_t entry;
	pgoff_t ilx;
	bool page_allocated;

	win = swap_vma_ra_win(vmf, &start, &end);
	if (win == 1)
		goto skip;

	ilx = targ_ilx - PFN_DOWN(vmf->address - start);

	blk_start_plug(&plug);
	for (addr = start; addr < end; ilx++, addr += PAGE_SIZE) {
		if (!pte++) {
			pte = pte_offset_map(vmf->pmd, addr);
			if (!pte)
				break;
		}
		pentry = ptep_get_lockless(pte);
		if (!is_swap_pte(pentry))
			continue;
		entry = pte_to_swp_entry(pentry);
		if (unlikely(non_swap_entry(entry)))
			continue;
		pte_unmap(pte);
		pte = NULL;
		folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
						&page_allocated, false);
		if (!folio)
			continue;
		if (page_allocated) {
			swap_read_folio(folio, &splug);
			if (addr != vmf->address) {
				folio_set_readahead(folio);
				count_vm_event(SWAP_RA);
			}
		}
		folio_put(folio);
	}
	if (pte)
		pte_unmap(pte);
	blk_finish_plug(&plug);
	swap_read_unplug(splug);
	lru_add_drain();
skip:
	/* The folio was likely read above, so no need for plugging here */
	folio = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
					&page_allocated, false);
	if (unlikely(page_allocated))
		swap_read_folio(folio, NULL);
	return folio;
}