swap: avoid a redundant pte map if ra window is 1

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

Link: https://lkml.kernel.org/r/20221219185840.25441-3-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 2927507b43d8192f876624199cb077cce7139242..af8bc123b7c45b6dd8742701d1cc188a533b71d9 100644 (file)
--- 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)