// 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#L709
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

static void swap_ra_info(struct vm_fault *vmf,
			struct vma_swap_readahead *ra_info)
{
	struct vm_area_struct *vma = vmf->vma;
	unsigned long ra_val;
	unsigned long faddr, pfn, fpfn;
	unsigned long start, end;
	pte_t *pte, *orig_pte;
	unsigned int max_win, hits, prev_win, win, left;
#ifndef CONFIG_64BIT
	pte_t *tpte;
#endif

	max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
			     SWAP_RA_ORDER_CEILING);
	if (max_win == 1) {
		ra_info->win = 1;
		return;
	}

	faddr = vmf->address;
	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);

	fpfn = PFN_DOWN(faddr);
	ra_val = GET_SWAP_RA_VAL(vma);
	pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
	prev_win = SWAP_RA_WIN(ra_val);
	hits = SWAP_RA_HITS(ra_val);
	ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
					       max_win, prev_win);
	atomic_long_set(&vma->swap_readahead_info,
			SWAP_RA_VAL(faddr, win, 0));

	if (win == 1) {
		pte_unmap(orig_pte);
		return;
	}

	/* Copy the PTEs because the page table may be unmapped */
	if (fpfn == pfn + 1)
		swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
	else if (pfn == fpfn + 1)
		swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
				  &start, &end);
	else {
		left = (win - 1) / 2;
		swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
				  &start, &end);
	}
	ra_info->nr_pte = end - start;
	ra_info->offset = fpfn - start;
	pte -= ra_info->offset;
#ifdef CONFIG_64BIT
	ra_info->ptes = pte;
#else
	tpte = ra_info->ptes;
	for (pfn = start; pfn != end; pfn++)
		*tpte++ = *pte++;
#endif
	pte_unmap(orig_pte);
}