The patch titled
Subject: mm/migrate: preserve exact soft-dirty state
has been added to the -mm mm-unstable branch. Its filename is
mm-migrate-preserve-exact-soft-dirty-state.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-preserve-exact-soft-dirty-state.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: Paul Gofman <pgofman@xxxxxxxxxxxxxxx>
Subject: mm/migrate: preserve exact soft-dirty state
Date: Tue, 6 Feb 2024 13:48:01 +0500
pte_mkdirty() sets both _PAGE_DIRTY and _PAGE_SOFT_DIRTY bits. The
_PAGE_SOFT_DIRTY can get set even if it wasn't set on original page before
migration. This makes non-soft-dirty pages soft-dirty just because of
migration/compaction. Clear the _PAGE_SOFT_DIRTY flag if it wasn't set on
original page.
By definition of soft-dirty feature, there can be spurious soft-dirty
pages because of kernel's internal activity such as VMA merging or
migration/compaction. This patch is eliminating the spurious soft-dirty
pages because of migration/compaction.
Link: https://lkml.kernel.org/r/20240206084838.34560-1-usama.anjum@xxxxxxxxxxxxx
Signed-off-by: Paul Gofman <pgofman@xxxxxxxxxxxxxxx>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Cc: MichaÅ? MirosÅ?aw <emmir@xxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/migrate.c~mm-migrate-preserve-exact-soft-dirty-state
+++ a/mm/migrate.c
@@ -211,14 +211,17 @@ static bool remove_migration_pte(struct
folio_get(folio);
pte = mk_pte(new, READ_ONCE(vma->vm_page_prot));
old_pte = ptep_get(pvmw.pte);
- if (pte_swp_soft_dirty(old_pte))
- pte = pte_mksoft_dirty(pte);
entry = pte_to_swp_entry(old_pte);
if (!is_migration_entry_young(entry))
pte = pte_mkold(pte);
if (folio_test_dirty(folio) && is_migration_entry_dirty(entry))
pte = pte_mkdirty(pte);
+ if (pte_swp_soft_dirty(old_pte))
+ pte = pte_mksoft_dirty(pte);
+ else
+ pte = pte_clear_soft_dirty(pte);
+
if (is_writable_migration_entry(entry))
pte = pte_mkwrite(pte, vma);
else if (pte_swp_uffd_wp(old_pte))
_
Patches currently in -mm which might be from pgofman@xxxxxxxxxxxxxxx are
mm-migrate-preserve-exact-soft-dirty-state.patch
