// 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#L607
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
				struct vm_fault *vmf)
{
	struct page *page;
	unsigned long entry_offset = swp_offset(entry);
	unsigned long offset = entry_offset;
	unsigned long start_offset, end_offset;
	unsigned long mask;
	struct swap_info_struct *si = swp_swap_info(entry);
	struct blk_plug plug;
	struct swap_iocb *splug = NULL;
	bool do_poll = true, page_allocated;
	struct vm_area_struct *vma = vmf->vma;
	unsigned long addr = vmf->address;

	mask = swapin_nr_pages(offset) - 1;
	if (!mask)
		goto skip;

	do_poll = false;
	/* Read a page_cluster sized and aligned cluster around offset. */
	start_offset = offset & ~mask;
	end_offset = offset | mask;
	if (!start_offset)	/* First page is swap header. */
		start_offset++;
	if (end_offset >= si->max)
		end_offset = si->max - 1;

	blk_start_plug(&plug);
	for (offset = start_offset; offset <= end_offset ; offset++) {
		/* Ok, do the async read-ahead now */
		page = __read_swap_cache_async(
			swp_entry(swp_type(entry), offset),
			gfp_mask, vma, addr, &page_allocated);
		if (!page)
			continue;
		if (page_allocated) {
			swap_readpage(page, false, &splug);
			if (offset != entry_offset) {
				SetPageReadahead(page);
				count_vm_event(SWAP_RA);
			}
		}
		put_page(page);
	}
	blk_finish_plug(&plug);
	swap_read_unplug(splug);

	lru_add_drain();	/* Push any new pages onto the LRU now */
skip:
	/* The page was likely read above, so no need for plugging here */
	return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll, NULL);
}