From: Kairui Song <kasong@xxxxxxxxxxx>
Some useful comments were dropped in commit b56a2d8af914 ('mm: rid
swapoff of quadratic complexity'), add them back.
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
mm/swapfile.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4bc70f459164..756104ebd585 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1879,6 +1879,17 @@ 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;
--
2.42.0
