The patch titled
Subject: mm/munlock: delete smp_mb() from __pagevec_lru_add_fn()
has been added to the -mm tree. Its filename is
mm-munlock-delete-smp_mb-from-__pagevec_lru_add_fn.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-munlock-delete-smp_mb-from-__pagevec_lru_add_fn.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-munlock-delete-smp_mb-from-__pagevec_lru_add_fn.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/munlock: delete smp_mb() from __pagevec_lru_add_fn()
My reading of comment on smp_mb__after_atomic() in __pagevec_lru_add_fn()
says that it can now be deleted; and that remains so when the next patch
is added.
Link: https://lkml.kernel.org/r/28a7c6ff-6270-9060-8df0-862bdcaac366@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap.c | 37 +++++++++----------------------------
1 file changed, 9 insertions(+), 28 deletions(-)
--- a/mm/swap.c~mm-munlock-delete-smp_mb-from-__pagevec_lru_add_fn
+++ a/mm/swap.c
@@ -1025,37 +1025,18 @@ static void __pagevec_lru_add_fn(struct
VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
+ folio_set_lru(folio);
/*
- * A folio becomes evictable in two ways:
- * 1) Within LRU lock [munlock_vma_page() and __munlock_pagevec()].
- * 2) Before acquiring LRU lock to put the folio on the correct LRU
- * and then
- * a) do PageLRU check with lock [check_move_unevictable_pages]
- * b) do PageLRU check before lock [clear_page_mlock]
- *
- * (1) & (2a) are ok as LRU lock will serialize them. For (2b), we need
- * following strict ordering:
- *
- * #0: __pagevec_lru_add_fn #1: clear_page_mlock
- *
- * folio_set_lru() folio_test_clear_mlocked()
- * smp_mb() // explicit ordering // above provides strict
- * // ordering
- * folio_test_mlocked() folio_test_lru()
+ * Is an smp_mb__after_atomic() still required here, before
+ * folio_evictable() tests PageMlocked, to rule out the possibility
+ * of stranding an evictable folio on an unevictable LRU? I think
+ * not, because munlock_page() only clears PageMlocked while the LRU
+ * lock is held.
*
- *
- * if '#1' does not observe setting of PG_lru by '#0' and
- * fails isolation, the explicit barrier will make sure that
- * folio_evictable check will put the folio on the correct
- * LRU. Without smp_mb(), folio_set_lru() can be reordered
- * after folio_test_mlocked() check and can make '#1' fail the
- * isolation of the folio whose mlocked bit is cleared (#0 is
- * also looking at the same folio) and the evictable folio will
- * be stranded on an unevictable LRU.
+ * (That is not true of __page_cache_release(), and not necessarily
+ * true of release_pages(): but those only clear PageMlocked after
+ * put_page_testzero() has excluded any other users of the page.)
*/
- folio_set_lru(folio);
- smp_mb__after_atomic();
-
if (folio_evictable(folio)) {
if (was_unevictable)
__count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-munlock-delete-page_mlock-and-all-its-works.patch
mm-munlock-delete-foll_mlock-and-foll_populate.patch
mm-munlock-delete-munlock_vma_pages_all-allow-oomreap.patch
mm-munlock-rmap-call-mlock_vma_page-munlock_vma_page.patch
mm-munlock-replace-clear_page_mlock-by-final-clearance.patch
mm-munlock-maintain-page-mlock_count-while-unevictable.patch
mm-munlock-mlock_pte_range-when-mlocking-or-munlocking.patch
mm-migrate-__unmap_and_move-push-good-newpage-to-lru.patch
mm-munlock-delete-smp_mb-from-__pagevec_lru_add_fn.patch
mm-munlock-mlock_page-munlock_page-batch-by-pagevec.patch
mm-munlock-page-migration-needs-mlock-pagevec-drained.patch
mm-thp-collapse_file-do-try_to_unmapttu_batch_flush.patch
mm-thp-shrink_page_list-avoid-splitting-vm_locked-thp.patch
