// 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#L785
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
				       struct vm_fault *vmf)
{
	struct blk_plug plug;
	struct swap_iocb *splug = NULL;
	struct vm_area_struct *vma = vmf->vma;
	struct page *page;
	pte_t *pte, pentry;
	swp_entry_t entry;
	unsigned int i;
	bool page_allocated;
	struct vma_swap_readahead ra_info = {
		.win = 1,
	};

	swap_ra_info(vmf, &ra_info);
	if (ra_info.win == 1)
		goto skip;

	blk_start_plug(&plug);
	for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
	     i++, pte++) {
		pentry = *pte;
		if (!is_swap_pte(pentry))
			continue;
		entry = pte_to_swp_entry(pentry);
		if (unlikely(non_swap_entry(entry)))
			continue;
		page = __read_swap_cache_async(entry, gfp_mask, vma,
					       vmf->address, &page_allocated);
		if (!page)
			continue;
		if (page_allocated) {
			swap_readpage(page, false, &splug);
			if (i != ra_info.offset) {
				SetPageReadahead(page);
				count_vm_event(SWAP_RA);
			}
		}
		put_page(page);
	}
	blk_finish_plug(&plug);
	swap_read_unplug(splug);
	lru_add_drain();
skip:
	/* The page was likely read above, so no need for plugging here */
	return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
				     ra_info.win == 1, NULL);
}