[to-be-updated] mm-thp-dont-have-to-lock-page-anymore-when-splitting-pmd.patch removed from -mm tree

[to-be-updated] mm-thp-dont-have-to-lock-page-anymore-when-splitting-pmd.patch removed from -mm tree

[Andrew Morton]

The patch titled
     Subject: mm: thp: don't have to lock page anymore when splitting PMD
has been removed from the -mm tree.  Its filename was
     mm-thp-dont-have-to-lock-page-anymore-when-splitting-pmd.patch

This patch was dropped because an updated version will be merged

------------------------------------------------------
From: Yang Shi <shy828301@gmail.com>
Subject: mm: thp: don't have to lock page anymore when splitting PMD

commit c444eb564fb1 ("mm: thp: make the THP mapcount atomic against
__split_huge_pmd_locked()") locked the page for PMD split to make mapcount
stable for reuse_swap_page(), then commit 1c2f67308af4 ("mm: thp: fix
MADV_REMOVE deadlock on shmem THP") reduce the scope to anonymous page
only.

However COW has not used mapcount to determine if the page is shared or
not anymore due to the COW fixes [1] from David Hildenbrand and the
reuse_swap_page() was removed as well.  So PMD split doesn't have to lock
the page anymore.  This patch basically reverted the above two commits.

[1] https://lore.kernel.org/linux-mm/20220131162940.210846-1-david@redhat.com/

Link: https://lkml.kernel.org/r/20220303222014.517033-1-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |   44 +++++---------------------------------------
 1 file changed, 5 insertions(+), 39 deletions(-)

--- a/mm/huge_memory.c~mm-thp-dont-have-to-lock-page-anymore-when-splitting-pmd
+++ a/mm/huge_memory.c
@@ -2126,8 +2126,6 @@ void __split_huge_pmd(struct vm_area_str
 {
 	spinlock_t *ptl;
 	struct mmu_notifier_range range;
-	bool do_unlock_folio = false;
-	pmd_t _pmd;
 
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
 				address & HPAGE_PMD_MASK,
@@ -2140,48 +2138,16 @@ void __split_huge_pmd(struct vm_area_str
 	 * pmd against. Otherwise we can end up replacing wrong folio.
 	 */
 	VM_BUG_ON(freeze && !folio);
-	if (folio) {
-		VM_WARN_ON_ONCE(!folio_test_locked(folio));
-		if (folio != page_folio(pmd_page(*pmd)))
-			goto out;
-	}
+	if (folio && folio != page_folio(pmd_page(*pmd)))
+		goto out;
 
-repeat:
-	if (pmd_trans_huge(*pmd)) {
-		if (!folio) {
-			folio = page_folio(pmd_page(*pmd));
-			/*
-			 * An anonymous page must be locked, to ensure that a
-			 * concurrent reuse_swap_page() sees stable mapcount;
-			 * but reuse_swap_page() is not used on shmem or file,
-			 * and page lock must not be taken when zap_pmd_range()
-			 * calls __split_huge_pmd() while i_mmap_lock is held.
-			 */
-			if (folio_test_anon(folio)) {
-				if (unlikely(!folio_trylock(folio))) {
-					folio_get(folio);
-					_pmd = *pmd;
-					spin_unlock(ptl);
-					folio_lock(folio);
-					spin_lock(ptl);
-					if (unlikely(!pmd_same(*pmd, _pmd))) {
-						folio_unlock(folio);
-						folio_put(folio);
-						folio = NULL;
-						goto repeat;
-					}
-					folio_put(folio);
-				}
-				do_unlock_folio = true;
-			}
-		}
-	} else if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
+	if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
 		goto out;
+
 	__split_huge_pmd_locked(vma, pmd, range.start, freeze);
 out:
 	spin_unlock(ptl);
-	if (do_unlock_folio)
-		folio_unlock(folio);
+
 	/*
 	 * No need to double call mmu_notifier->invalidate_range() callback.
 	 * They are 3 cases to consider inside __split_huge_pmd_locked():
_

Patches currently in -mm which might be from shy828301@gmail.com are