From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Alistair Popple <apopple@nvidia.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@surriel.com>,
Suren Baghdasaryan <surenb@google.com>,
Yu Zhao <yuzhao@google.com>, Greg Thelen <gthelen@google.com>,
Shakeel Butt <shakeelb@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH v2 09/13] mm/munlock: delete smp_mb() from __pagevec_lru_add_fn()
Date: Mon, 14 Feb 2022 18:34:46 -0800 (PST) [thread overview]
Message-ID: <28a7c6ff-6270-9060-8df0-862bdcaac366@google.com> (raw)
In-Reply-To: <55a49083-37f9-3766-1de9-9feea7428ac@google.com>
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.
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
v2: same as v1.
mm/swap.c | 37 +++++++++----------------------------
1 file changed, 9 insertions(+), 28 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c
index 682a03301a2c..3f770b1ea2c1 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -1025,37 +1025,18 @@ static void __pagevec_lru_add_fn(struct folio *folio, struct lruvec *lruvec)
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);
--
2.34.1
next prev parent reply other threads:[~2022-02-15 2:34 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-15 2:18 [PATCH v2 00/13] mm/munlock: rework of mlock+munlock page handling Hugh Dickins
2022-02-15 2:20 ` [PATCH v2 01/13] mm/munlock: delete page_mlock() and all its works Hugh Dickins
2022-02-15 2:21 ` [PATCH v2 02/13] mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE Hugh Dickins
2022-02-15 2:23 ` [PATCH v2 03/13] mm/munlock: delete munlock_vma_pages_all(), allow oomreap Hugh Dickins
2022-02-15 2:26 ` [PATCH v2 04/13] mm/munlock: rmap call mlock_vma_page() munlock_vma_page() Hugh Dickins
2022-02-15 15:22 ` Matthew Wilcox
2022-02-15 21:38 ` Hugh Dickins
2022-02-15 23:21 ` Matthew Wilcox
2022-02-15 2:28 ` [PATCH v2 05/13] mm/munlock: replace clear_page_mlock() by final clearance Hugh Dickins
2022-02-15 2:29 ` [PATCH v2 06/13] mm/munlock: maintain page->mlock_count while unevictable Hugh Dickins
2022-02-15 2:31 ` [PATCH v2 07/13] mm/munlock: mlock_pte_range() when mlocking or munlocking Hugh Dickins
2022-02-18 6:35 ` [mm/munlock] 237b445401: stress-ng.remap.ops_per_sec -62.6% regression kernel test robot
2022-02-18 8:49 ` Hugh Dickins
2022-02-21 6:32 ` Hugh Dickins
2022-02-24 8:37 ` Oliver Sang
2022-02-15 2:33 ` [PATCH v2 08/13] mm/migrate: __unmap_and_move() push good newpage to LRU Hugh Dickins
2022-02-15 2:34 ` Hugh Dickins [this message]
2022-02-15 2:37 ` [PATCH v2 10/13] mm/munlock: mlock_page() munlock_page() batch by pagevec Hugh Dickins
2022-02-15 16:40 ` Matthew Wilcox
2022-02-15 21:02 ` Hugh Dickins
2022-02-15 22:56 ` Matthew Wilcox
2022-02-15 2:38 ` [PATCH v2 11/13] mm/munlock: page migration needs mlock pagevec drained Hugh Dickins
2022-02-15 2:40 ` [PATCH v2 12/13] mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH) Hugh Dickins
2022-02-15 2:42 ` [PATCH v2 13/13] mm/thp: shrink_page_list() avoid splitting VM_LOCKED THP Hugh Dickins
2022-02-15 19:35 ` [PATCH v2 00/13] mm/munlock: rework of mlock+munlock page handling Matthew Wilcox
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