mm: factor out a swap_readpage_bdev helper

Split the block device case from swap_readpage into a separate helper,
following the abstraction for file based swap and frontswap.

Link: https://lkml.kernel.org/r/20230125133436.447864-4-hch@lst.de
Signed-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

@@ -444,44 +444,15 @@ static void swap_readpage_fs(struct page *page,
 		*plug = sio;
 }
 
-void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
+static void swap_readpage_bdev(struct page *page, bool synchronous,
+		struct swap_info_struct *sis)
 {
 	struct bio *bio;
-	struct swap_info_struct *sis = page_swap_info(page);
-	bool workingset = PageWorkingset(page);
-	unsigned long pflags;
-	bool in_thrashing;
-
-	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
-	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	VM_BUG_ON_PAGE(PageUptodate(page), page);
-
-	/*
-	 * Count submission time as memory stall and delay. When the device
-	 * is congested, or the submitting cgroup IO-throttled, submission
-	 * can be a significant part of overall IO time.
-	 */
-	if (workingset) {
-		delayacct_thrashing_start(&in_thrashing);
-		psi_memstall_enter(&pflags);
-	}
-	delayacct_swapin_start();
-
-	if (frontswap_load(page) == 0) {
-		SetPageUptodate(page);
-		unlock_page(page);
-		goto out;
-	}
-
-	if (data_race(sis->flags & SWP_FS_OPS)) {
-		swap_readpage_fs(page, plug);
-		goto out;
-	}
 
 	if ((sis->flags & SWP_SYNCHRONOUS_IO) &&
 	    !bdev_read_page(sis->bdev, swap_page_sector(page), page)) {
 		count_vm_event(PSWPIN);
-		goto out;
+		return;
 	}
 
 	bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
@@ -508,8 +479,39 @@ void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
 	}
 	__set_current_state(TASK_RUNNING);
 	bio_put(bio);
+}
+
+void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
+{
+	struct swap_info_struct *sis = page_swap_info(page);
+	bool workingset = PageWorkingset(page);
+	unsigned long pflags;
+	bool in_thrashing;
+
+	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(PageUptodate(page), page);
+
+	/*
+	 * Count submission time as memory stall and delay. When the device
+	 * is congested, or the submitting cgroup IO-throttled, submission
+	 * can be a significant part of overall IO time.
+	 */
+	if (workingset) {
+		delayacct_thrashing_start(&in_thrashing);
+		psi_memstall_enter(&pflags);
+	}
+	delayacct_swapin_start();
+
+	if (frontswap_load(page) == 0) {
+		SetPageUptodate(page);
+		unlock_page(page);
+	} else if (data_race(sis->flags & SWP_FS_OPS)) {
+		swap_readpage_fs(page, plug);
+	} else {
+		swap_readpage_bdev(page, synchronous, sis);
+	}
 
-out:
 	if (workingset) {
 		delayacct_thrashing_end(&in_thrashing);
 		psi_memstall_leave(&pflags);