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

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Date:   Tue, 20 Dec 2022 02:58:38 +0800
From:   Kairui Song <ryncsn@...il.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Kairui Song <kasong@...cent.com>
Subject: [PATCH v2 2/4] swap: avoid a redundant pte map if ra window is 1

From: Kairui Song <kasong@...cent.com>

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

Signed-off-by: Kairui Song <kasong@...cent.com>
Reviewed-by: "Huang, Ying" <ying.huang@...el.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