[PATCH v2 2/4] swap: avoid a redundant pte map if ra window is 1

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

Avoid a redundant pte map/unmap when swap readahead window is 1.

Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/swap_state.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 2927507b43d8..af8bc123b7c4 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -727,8 +727,6 @@ static void swap_ra_info(struct vm_fault *vmf,
 	}
 
 	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));
@@ -739,12 +737,11 @@ static void swap_ra_info(struct vm_fault *vmf,
 	atomic_long_set(&vma->swap_readahead_info,
 			SWAP_RA_VAL(faddr, win, 0));
 
-	if (win == 1) {
-		pte_unmap(orig_pte);
+	if (win == 1)
 		return;
-	}
 
 	/* Copy the PTEs because the page table may be unmapped */
+	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
 	if (fpfn == pfn + 1)
 		swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
 	else if (pfn == fpfn + 1)
-- 
2.35.2