The patch titled
Subject: mm,thp,rmap: clean up the end of __split_huge_pmd_locked()
has been added to the -mm mm-unstable branch. Its filename is
mmthprmap-clean-up-the-end-of-__split_huge_pmd_locked.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmthprmap-clean-up-the-end-of-__split_huge_pmd_locked.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: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm,thp,rmap: clean up the end of __split_huge_pmd_locked()
Date: Tue, 22 Nov 2022 01:51:50 -0800 (PST)
It's hard to add a page_add_anon_rmap() into __split_huge_pmd_locked()'s
HPAGE_PMD_NR set_pte_at() loop, without wincing at the "freeze" case's
HPAGE_PMD_NR page_remove_rmap() loop below it.
It's just a mistake to add rmaps in the "freeze" (insert migration entries
prior to splitting huge page) case: the pmd_migration case already avoids
doing that, so just follow its lead. page_add_ref() versus put_page()
likewise. But why is one more put_page() needed in the "freeze" case?
Because it's removing the pmd rmap, already removed when pmd_migration
(and freeze and pmd_migration are mutually exclusive cases).
Link: https://lkml.kernel.org/r/d43748aa-fece-e0b9-c4ab-f23c9ebc9011@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Dan Carpenter <error27@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mina Almasry <almasrymina@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)
--- a/mm/huge_memory.c~mmthprmap-clean-up-the-end-of-__split_huge_pmd_locked
+++ a/mm/huge_memory.c
@@ -2095,7 +2095,6 @@ static void __split_huge_pmd_locked(stru
uffd_wp = pmd_uffd_wp(old_pmd);
VM_BUG_ON_PAGE(!page_count(page), page);
- page_ref_add(page, HPAGE_PMD_NR - 1);
/*
* Without "freeze", we'll simply split the PMD, propagating the
@@ -2115,6 +2114,8 @@ static void __split_huge_pmd_locked(stru
anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
if (freeze && anon_exclusive && page_try_share_anon_rmap(page))
freeze = false;
+ if (!freeze)
+ page_ref_add(page, HPAGE_PMD_NR - 1);
}
/*
@@ -2170,27 +2171,21 @@ static void __split_huge_pmd_locked(stru
entry = pte_mksoft_dirty(entry);
if (uffd_wp)
entry = pte_mkuffd_wp(entry);
+ page_add_anon_rmap(page + i, vma, addr, false);
}
pte = pte_offset_map(&_pmd, addr);
BUG_ON(!pte_none(*pte));
set_pte_at(mm, addr, pte, entry);
- if (!pmd_migration)
- page_add_anon_rmap(page + i, vma, addr, false);
pte_unmap(pte);
}
if (!pmd_migration)
page_remove_rmap(page, vma, true);
+ if (freeze)
+ put_page(page);
smp_wmb(); /* make pte visible before pmd */
pmd_populate(mm, pmd, pgtable);
-
- if (freeze) {
- for (i = 0; i < HPAGE_PMD_NR; i++) {
- page_remove_rmap(page + i, vma, false);
- put_page(page + i);
- }
- }
}
void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mmhugetlb-use-folio-fields-in-second-tail-page.patch
mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch
mmthprmap-simplify-compound-page-mapcount-handling.patch
mmthprmap-lock_compound_mapcounts-on-thp-mapcounts.patch
mmthprmap-handle-the-normal-pagecompound-case-first.patch
mmthprmap-subpages_mapcount-of-pte-mapped-subpages.patch
mmthprmap-subpages_mapcount-compound_mapped-if-pmd-mapped.patch
mmthprmap-clean-up-the-end-of-__split_huge_pmd_locked.patch
