swap: rename SWP_FS to SWAP_FS_OPS to avoid ambiguity

SWP_FS is used to make swap_{read,write}page() go through the filesystem,
and it's only used for swap files over NFS for now.  Otherwise it will
directly submit IO to blockdev according to swapfile extents reported by
filesystems in advance.

As Matthew pointed out [1], SWP_FS naming is somewhat confusing, so let's
rename to SWP_FS_OPS.

[1] https://lore.kernel.org/r/[email protected]

Suggested-by: Matthew Wilcox <[email protected]>
Signed-off-by: Gao Xiang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/mm/page_io.c b/mm/page_io.c
index f9e9267..2ffe4c4 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -312,7 +312,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	struct swap_info_struct *sis = page_swap_info(page);
 
 	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
-	if (data_race(sis->flags & SWP_FS)) {
+	if (data_race(sis->flags & SWP_FS_OPS)) {
 		struct kiocb kiocb;
 		struct file *swap_file = sis->swap_file;
 		struct address_space *mapping = swap_file->f_mapping;
@@ -403,7 +403,7 @@ int swap_readpage(struct page *page, bool synchronous)
 		goto out;
 	}
 
-	if (data_race(sis->flags & SWP_FS)) {
+	if (data_race(sis->flags & SWP_FS_OPS)) {
 		struct file *swap_file = sis->swap_file;
 		struct address_space *mapping = swap_file->f_mapping;
 
@@ -467,7 +467,7 @@ int swap_set_page_dirty(struct page *page)
 {
 	struct swap_info_struct *sis = page_swap_info(page);
 
-	if (data_race(sis->flags & SWP_FS)) {
+	if (data_race(sis->flags & SWP_FS_OPS)) {
 		struct address_space *mapping = sis->swap_file->f_mapping;
 
 		VM_BUG_ON_PAGE(!PageSwapCache(page), page);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index f24f2cea..aa40e70 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -665,7 +665,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
 		goto skip;
 
 	/* Test swap type to make sure the dereference is safe */
-	if (likely(si->flags & (SWP_BLKDEV | SWP_FS))) {
+	if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) {
 		struct inode *inode = si->swap_file->f_mapping->host;
 		if (inode_read_congested(inode))
 			goto skip;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index ced4635..183b87b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2437,7 +2437,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 		if (ret >= 0)
 			sis->flags |= SWP_ACTIVATED;
 		if (!ret) {
-			sis->flags |= SWP_FS;
+			sis->flags |= SWP_FS_OPS;
 			ret = add_swap_extent(sis, 0, sis->max, 0);
 			*span = sis->pages;
 		}