diff mbox series

[02/24] mm/swapfile.c: add back some comment

Message ID 20231119194740.94101-3-ryncsn@gmail.com
State New
Headers
Series Swapin path refactor for optimization and bugfix |

Commit Message

Kairui Song Nov. 19, 2023, 7:47 p.m. UTC 
  From: Kairui Song <kasong@tencent.com>

Some useful comments were dropped in commit b56a2d8af914 ('mm: rid
swapoff of quadratic complexity'), add them back.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/swapfile.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
diff mbox series

Patch

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;