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Message-ID: <20240129175423.1987-2-ryncsn@gmail.com>
Date: Tue, 30 Jan 2024 01:54:16 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Chris Li <chrisl@...nel.org>,
"Huang, Ying" <ying.huang@...el.com>,
Hugh Dickins <hughd@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Matthew Wilcox <willy@...radead.org>,
Michal Hocko <mhocko@...e.com>,
Yosry Ahmed <yosryahmed@...gle.com>,
David Hildenbrand <david@...hat.com>,
linux-kernel@...r.kernel.org,
Kairui Song <kasong@...cent.com>
Subject: [PATCH v3 1/7] mm/swapfile.c: add back some comment
From: Kairui Song <kasong@...cent.com>
Some useful comments were dropped in commit b56a2d8af914 ("mm: rid
swapoff of quadratic complexity"), add them back.
Signed-off-by: Kairui Song <kasong@...cent.com>
---
mm/swapfile.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 0008cd39af42..606d95b56304 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1881,6 +1881,17 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
folio = page_folio(page);
}
if (!folio) {
+ /*
+ * The entry could have been freed, and will not
+ * be reused since swapoff() already disabled
+ * allocation from here, or alloc_page() failed.
+ *
+ * We don't hold lock here, so the swap entry could be
+ * SWAP_MAP_BAD (when the cluster is discarding).
+ * Instead of fail out, We can just skip the swap
+ * entry because swapoff will wait for discarding
+ * finish anyway.
+ */
swp_count = READ_ONCE(si->swap_map[offset]);
if (swp_count == 0 || swp_count == SWAP_MAP_BAD)
continue;
--
2.43.0
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