mm: remove the swap_readpage return value

swap_readpage always returns 0, and no caller checks the return value.

[akpm@linux-foundation.org: fix void-returning swap_readpage() stub, per Keith]
Link: https://lkml.kernel.org/r/20230125133436.447864-3-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_io.c

@@ -444,11 +444,9 @@ static void swap_readpage_fs(struct page *page,
 		*plug = sio;
 }
 
-int swap_readpage(struct page *page, bool synchronous,
-		  struct swap_iocb **plug)
+void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
 {
 	struct bio *bio;
-	int ret = 0;
 	struct swap_info_struct *sis = page_swap_info(page);
 	bool workingset = PageWorkingset(page);
 	unsigned long pflags;
@@ -480,15 +478,12 @@ int swap_readpage(struct page *page, bool synchronous,
 		goto out;
 	}
 
-	if (sis->flags & SWP_SYNCHRONOUS_IO) {
-		ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
-		if (!ret) {
-			count_vm_event(PSWPIN);
-			goto out;
-		}
+	if ((sis->flags & SWP_SYNCHRONOUS_IO) &&
+	    !bdev_read_page(sis->bdev, swap_page_sector(page), page)) {
+		count_vm_event(PSWPIN);
+		goto out;
 	}
 
-	ret = 0;
 	bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
 	bio->bi_iter.bi_sector = swap_page_sector(page);
 	bio->bi_end_io = end_swap_bio_read;
@@ -520,7 +515,6 @@ int swap_readpage(struct page *page, bool synchronous,
 		psi_memstall_leave(&pflags);
 	}
 	delayacct_swapin_end();
-	return ret;
 }
 
 void __swap_read_unplug(struct swap_iocb *sio)

mm/swap.h

@@ -8,8 +8,7 @@
 /* linux/mm/page_io.c */
 int sio_pool_init(void);
 struct swap_iocb;
-int swap_readpage(struct page *page, bool do_poll,
-		  struct swap_iocb **plug);
+void swap_readpage(struct page *page, bool do_poll, struct swap_iocb **plug);
 void __swap_read_unplug(struct swap_iocb *plug);
 static inline void swap_read_unplug(struct swap_iocb *plug)
 {
@@ -64,10 +63,9 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
 }
 #else /* CONFIG_SWAP */
 struct swap_iocb;
-static inline int swap_readpage(struct page *page, bool do_poll,
-				struct swap_iocb **plug)
+static inline void swap_readpage(struct page *page, bool do_poll,
+		struct swap_iocb **plug)
 {
-	return 0;
 }
 static inline void swap_write_unplug(struct swap_iocb *sio)
 {