[PATCH 4/9] mm: swap: remove unneeded VM_BUG_ON(*map != SWAP_HAS_CACHE) in swap_entry_range_free()

[Kemeng Shi]

As all callers of swap_entry_range_free() have already ensured slots to
be freed are marked as SWAP_HAS_CACHE while holding the cluster lock,
the BUG_ON check can be safely removed. After this, the function
swap_entry_range_free() could drop any kind of last flag, rename it to
swap_entries_free() and update it's comment accordingly.

This is a preparation to use swap_entries_free() to drop last 1 and
SWAP_MAP_SHMEM flag.

Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
---
 mm/swapfile.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index ba37b9bff586..14b7b37996ff 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -52,9 +52,9 @@
 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
 				 unsigned char);
 static void free_swap_count_continuations(struct swap_info_struct *);
-static void swap_entry_range_free(struct swap_info_struct *si,
-				  struct swap_cluster_info *ci,
-				  swp_entry_t entry, unsigned int nr_pages);
+static void swap_entries_free(struct swap_info_struct *si,
+			      struct swap_cluster_info *ci,
+			      swp_entry_t entry, unsigned int nr_pages);
 static void swap_range_alloc(struct swap_info_struct *si,
 			     unsigned int nr_entries);
 static bool folio_swapcache_freeable(struct folio *folio);
@@ -1511,7 +1511,7 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
 	for (i = 0; i < nr; i++)
 		WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
 	if (!has_cache)
-		swap_entry_range_free(si, ci, entry, nr);
+		swap_entries_free(si, ci, entry, nr);
 	unlock_cluster(ci);
 
 	return has_cache;
@@ -1530,12 +1530,12 @@ static bool swap_entries_put_nr(struct swap_info_struct *si,
 }
 
 /*
- * Drop the last HAS_CACHE flag of swap entries, caller have to
- * ensure all entries belong to the same cgroup.
+ * Drop the last flag(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries,
+ * caller have to ensure all entries belong to the same cgroup.
  */
-static void swap_entry_range_free(struct swap_info_struct *si,
-				  struct swap_cluster_info *ci,
-				  swp_entry_t entry, unsigned int nr_pages)
+static void swap_entries_free(struct swap_info_struct *si,
+			      struct swap_cluster_info *ci,
+			      swp_entry_t entry, unsigned int nr_pages)
 {
 	unsigned long offset = swp_offset(entry);
 	unsigned char *map = si->swap_map + offset;
@@ -1545,7 +1545,6 @@ static void swap_entry_range_free(struct swap_info_struct *si,
 	VM_BUG_ON(ci != offset_to_cluster(si, offset + nr_pages - 1));
 
 	do {
-		VM_BUG_ON(*map != SWAP_HAS_CACHE);
 		*map = 0;
 	} while (++map < map_end);
 
@@ -1605,7 +1604,7 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
 
 	ci = lock_cluster(si, offset);
 	if (swap_only_has_cache(si, offset, size))
-		swap_entry_range_free(si, ci, entry, size);
+		swap_entries_free(si, ci, entry, size);
 	else
 		for (int i = 0; i < size; i++, entry.val++)
 			swap_entry_put_locked(si, ci, entry, SWAP_HAS_CACHE);
-- 
2.30.0