[PATCH v2 6/8] mm/swap: get the swap file offset directly

[Kairui Song]

From: Kairui Song <kasong@xxxxxxxxxxx>

folio_file_pos and page_file_offset are for mixed usage of swap cache
and page cache, it can't be page cache here, so introduce a new helper
to get the swap offset in swap file directly.

Need to include swapops.h in mm/swap.h to ensure swp_offset is always
defined before use.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/page_io.c | 6 +++---
 mm/swap.h    | 9 +++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index ae2b49055e43..615812cfe4ca 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -279,7 +279,7 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 		 * be temporary.
 		 */
 		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
-				   ret, page_file_offset(page));
+				   ret, swap_dev_pos(page_swap_entry(page)));
 		for (p = 0; p < sio->pages; p++) {
 			page = sio->bvec[p].bv_page;
 			set_page_dirty(page);
@@ -298,7 +298,7 @@ static void swap_writepage_fs(struct folio *folio, struct writeback_control *wbc
 	struct swap_iocb *sio = NULL;
 	struct swap_info_struct *sis = swp_swap_info(folio->swap);
 	struct file *swap_file = sis->swap_file;
-	loff_t pos = folio_file_pos(folio);
+	loff_t pos = swap_dev_pos(folio->swap);
 
 	count_swpout_vm_event(folio);
 	folio_start_writeback(folio);
@@ -429,7 +429,7 @@ static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
 {
 	struct swap_info_struct *sis = swp_swap_info(folio->swap);
 	struct swap_iocb *sio = NULL;
-	loff_t pos = folio_file_pos(folio);
+	loff_t pos = swap_dev_pos(folio->swap);
 
 	if (plug)
 		sio = *plug;
diff --git a/mm/swap.h b/mm/swap.h
index fc2f6ade7f80..82023ab93205 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -5,6 +5,7 @@
 struct mempolicy;
 
 #ifdef CONFIG_SWAP
+#include <linux/swapops.h> /* for swp_offset */
 #include <linux/blk_types.h> /* for bio_end_io_t */
 
 /* linux/mm/page_io.c */
@@ -31,6 +32,14 @@ extern struct address_space *swapper_spaces[];
 	(&swapper_spaces[swp_type(entry)][swp_offset(entry) \
 		>> SWAP_ADDRESS_SPACE_SHIFT])
 
+/*
+ * Return the swap device position of the swap entry.
+ */
+static inline loff_t swap_dev_pos(swp_entry_t entry)
+{
+	return ((loff_t)swp_offset(entry)) << PAGE_SHIFT;
+}
+
 void show_swap_cache_info(void);
 bool add_to_swap(struct folio *folio);
 void *get_shadow_from_swap_cache(swp_entry_t entry);
-- 
2.44.0