mm,swap: simplify VMA based swap readahead window calculation

Replace PFNs with addresses in readahead window calculation.  This
simplified the logic and reduce the code line number.

No functionality change is expected.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 25 insertions, 41 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index eb7a306a2424..0803eedeabe3 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -741,54 +741,40 @@ void exit_swap_address_space(unsigned int type)
 	swapper_spaces[type] = NULL;
 }
 
-static unsigned short swap_vma_ra_win(struct vm_fault *vmf,
-				      unsigned short *offset,
-				      unsigned short *nr_pte)
+static int swap_vma_ra_win(struct vm_fault *vmf, unsigned long *start,
+			   unsigned long *end)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	unsigned long ra_val;
-	unsigned long faddr, pfn, fpfn, lpfn, rpfn;
-	unsigned long start, end;
+	unsigned long faddr, prev_faddr, left, right;
 	unsigned int max_win, hits, prev_win, win;
 
-	max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
-			     SWAP_RA_ORDER_CEILING);
+	max_win = 1 << min(READ_ONCE(page_cluster), SWAP_RA_ORDER_CEILING);
 	if (max_win == 1)
 		return 1;
 
 	faddr = vmf->address;
-	fpfn = PFN_DOWN(faddr);
 	ra_val = GET_SWAP_RA_VAL(vma);
-	pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
+	prev_faddr = SWAP_RA_ADDR(ra_val);
 	prev_win = SWAP_RA_WIN(ra_val);
 	hits = SWAP_RA_HITS(ra_val);
-	win = __swapin_nr_pages(pfn, fpfn, hits, max_win, prev_win);
-	atomic_long_set(&vma->swap_readahead_info,
-			SWAP_RA_VAL(faddr, win, 0));
+	win = __swapin_nr_pages(PFN_DOWN(prev_faddr), PFN_DOWN(faddr), hits,
+				max_win, prev_win);
+	atomic_long_set(&vma->swap_readahead_info, SWAP_RA_VAL(faddr, win, 0));
 	if (win == 1)
 		return 1;
 
-	if (fpfn == pfn + 1) {
-		lpfn = fpfn;
-		rpfn = fpfn + win;
-	} else if (pfn == fpfn + 1) {
-		lpfn = fpfn - win + 1;
-		rpfn = fpfn + 1;
-	} else {
-		unsigned int left = (win - 1) / 2;
-
-		lpfn = fpfn - left;
-		rpfn = fpfn + win - left;
-	}
-	if ((long)lpfn < 0)
-		lpfn = 0;
-	start = max3(lpfn, PFN_DOWN(vma->vm_start),
-		     PFN_DOWN(faddr & PMD_MASK));
-	end = min3(rpfn, PFN_DOWN(vma->vm_end),
-		   PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
-
-	*nr_pte = end - start;
-	*offset = fpfn - start;
+	if (faddr == prev_faddr + PAGE_SIZE)
+		left = faddr;
+	else if (prev_faddr == faddr + PAGE_SIZE)
+		left = faddr - (win << PAGE_SHIFT) + PAGE_SIZE;
+	else
+		left = faddr - (((win - 1) / 2) << PAGE_SHIFT);
+	right = left + (win << PAGE_SHIFT);
+	if ((long)left < 0)
+		left = 0;
+	*start = max3(left, vma->vm_start, faddr & PMD_MASK);
+	*end = min3(right, vma->vm_end, (faddr & PMD_MASK) + PMD_SIZE);
 
 	return win;
 }
@@ -816,22 +802,20 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 	struct swap_iocb *splug = NULL;
 	struct folio *folio;
 	pte_t *pte = NULL, pentry;
-	unsigned long addr;
+	int win;
+	unsigned long start, end, addr;
 	swp_entry_t entry;
 	pgoff_t ilx;
-	unsigned int i;
 	bool page_allocated;
-	unsigned short win, nr_pte, offset;
 
-	win = swap_vma_ra_win(vmf, &offset, &nr_pte);
+	win = swap_vma_ra_win(vmf, &start, &end);
 	if (win == 1)
 		goto skip;
 
-	addr = vmf->address - offset * PAGE_SIZE;
-	ilx = targ_ilx - offset;
+	ilx = targ_ilx - PFN_DOWN(vmf->address - start);
 
 	blk_start_plug(&plug);
-	for (i = 0; i < nr_pte; i++, ilx++, addr += PAGE_SIZE) {
+	for (addr = start; addr < end; ilx++, addr += PAGE_SIZE) {
 		if (!pte++) {
 			pte = pte_offset_map(vmf->pmd, addr);
 			if (!pte)
@@ -851,7 +835,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 			continue;
 		if (page_allocated) {
 			swap_read_folio(folio, false, &splug);
-			if (i != offset) {
+			if (addr != vmf->address) {
 				folio_set_readahead(folio);
 				count_vm_event(SWAP_RA);
 			}