[RFC PATCH 04/11] shmem: return number of pages beeing freed in shmem_free_swap

[Daniel Gomez]

Both shmem_free_swap callers expect the number of pages being freed. In
the large folios context, this needs to support larger values other than
0 (used as 1 page being freed) and -ENOENT (used as 0 pages being
freed). In preparation for large folios adoption, make shmem_free_swap
routine return the number of pages being freed. So, returning 0 in this
context, means 0 pages being freed.

Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>
Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
 mm/shmem.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index a2ac425b97ea..9f4c9b9286e5 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -827,18 +827,22 @@ static void shmem_delete_from_page_cache(struct folio *folio, void *radswap)
 }
 
 /*
- * Remove swap entry from page cache, free the swap and its page cache.
+ * Remove swap entry from page cache, free the swap and its page cache. Returns
+ * the number of pages being freed. 0 means entry not found in XArray (0 pages
+ * being freed).
  */
-static int shmem_free_swap(struct address_space *mapping,
+static long shmem_free_swap(struct address_space *mapping,
 			   pgoff_t index, void *radswap)
 {
 	void *old;
+	long swaps_freed = 1UL << xa_get_order(&mapping->i_pages, index);
 
 	old = xa_cmpxchg_irq(&mapping->i_pages, index, radswap, NULL, 0);
 	if (old != radswap)
-		return -ENOENT;
+		return 0;
 	free_swap_and_cache(radix_to_swp_entry(radswap));
-	return 0;
+
+	return swaps_freed;
 }
 
 /*
@@ -990,7 +994,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 			if (xa_is_value(folio)) {
 				if (unfalloc)
 					continue;
-				nr_swaps_freed += !shmem_free_swap(mapping,
+				nr_swaps_freed += shmem_free_swap(mapping,
 							indices[i], folio);
 				continue;
 			}
@@ -1057,14 +1061,17 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 			folio = fbatch.folios[i];
 
 			if (xa_is_value(folio)) {
+				long swaps_freed;
+
 				if (unfalloc)
 					continue;
-				if (shmem_free_swap(mapping, indices[i], folio)) {
+				swaps_freed = shmem_free_swap(mapping, indices[i], folio);
+				if (!swaps_freed) {
 					/* Swap was replaced by page: retry */
 					index = indices[i];
 					break;
 				}
-				nr_swaps_freed++;
+				nr_swaps_freed += swaps_freed;
 				continue;
 			}
 
-- 
2.39.2