Commit 055267fe authored by Paul Gofman's avatar Paul Gofman Committed by Andrew Morton
Browse files

mm/migrate: preserve exact soft-dirty state 

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@collabora.com


Signed-off-by: default avatarPaul Gofman <pgofman@codeweavers.com>
Signed-off-by: default avatarMuhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: default avatarAndrei Vagin <avagin@gmail.com>
Cc: Michał Mirosław <emmir@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a230c20e

mm/migrate.c

+5 −2
Original line number Diff line number Diff line
@@ -211,14 +211,17 @@ static bool remove_migration_pte(struct folio *folio, 
		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))