+ swap-avoid-a-redundant-pte-map-if-ra-window-is-1.patch added to mm-unstable branch

+ swap-avoid-a-redundant-pte-map-if-ra-window-is-1.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: swap: avoid a redundant pte map if ra window is 1
has been added to the -mm mm-unstable branch.  Its filename is
     swap-avoid-a-redundant-pte-map-if-ra-window-is-1.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/swap-avoid-a-redundant-pte-map-if-ra-window-is-1.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: swap: avoid a redundant pte map if ra window is 1
Date: Tue, 20 Dec 2022 02:58:38 +0800

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>
---

 mm/swap_state.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/mm/swap_state.c~swap-avoid-a-redundant-pte-map-if-ra-window-is-1
+++ a/mm/swap_state.c
@@ -727,8 +727,6 @@ static void swap_ra_info(struct vm_fault
 	}
 
 	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
 	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)
_

Patches currently in -mm which might be from kasong@tencent.com are

swapfile-get-rid-of-volatile-and-avoid-redundant-read.patch
swap-avoid-a-redundant-pte-map-if-ra-window-is-1.patch
swap-fold-swap_ra_clamp_pfn-into-swap_ra_info.patch
swap-avoid-holding-swap-reference-in-swap_cache_get_folio.patch