swapon(2)/swapoff(2): don't bother with block size

once upon a time that used to matter; these days we do swap IO for
swap devices at the level that doesn't give a damn about block size,
buffer_head or anything of that sort - just attach the page to
bio, set the location and size (the latter to PAGE_SIZE) and feed
into queue.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/swap.h

@@ -301,7 +301,6 @@ struct swap_info_struct {
 	struct file *bdev_file;		/* open handle of the bdev */
 	struct block_device *bdev;	/* swap device or bdev of swap file */
 	struct file *swap_file;		/* seldom referenced */
-	unsigned int old_block_size;	/* seldom referenced */
 	struct completion comp;		/* seldom referenced */
 	spinlock_t lock;		/*
 					 * protect map scan related fields like

mm/swapfile.c

@@ -2417,7 +2417,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	struct inode *inode;
 	struct filename *pathname;
 	int err, found = 0;
-	unsigned int old_block_size;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -2529,7 +2528,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	}
 
 	swap_file = p->swap_file;
-	old_block_size = p->old_block_size;
 	p->swap_file = NULL;
 	p->max = 0;
 	swap_map = p->swap_map;
@@ -2553,7 +2551,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 
 	inode = mapping->host;
 	if (p->bdev_file) {
-		set_blocksize(p->bdev, old_block_size);
 		fput(p->bdev_file);
 		p->bdev_file = NULL;
 	}
@@ -2782,21 +2779,15 @@ static struct swap_info_struct *alloc_swap_info(void)
 
 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
 {
-	int error;
-
 	if (S_ISBLK(inode->i_mode)) {
 		p->bdev_file = bdev_file_open_by_dev(inode->i_rdev,
 				BLK_OPEN_READ | BLK_OPEN_WRITE, p, NULL);
 		if (IS_ERR(p->bdev_file)) {
-			error = PTR_ERR(p->bdev_file);
+			int error = PTR_ERR(p->bdev_file);
 			p->bdev_file = NULL;
 			return error;
 		}
 		p->bdev = file_bdev(p->bdev_file);
-		p->old_block_size = block_size(p->bdev);
-		error = set_blocksize(p->bdev, PAGE_SIZE);
-		if (error < 0)
-			return error;
 		/*
 		 * Zoned block devices contain zones that have a sequential
 		 * write only restriction.  Hence zoned block devices are not
@@ -3235,7 +3226,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	free_percpu(p->cluster_next_cpu);
 	p->cluster_next_cpu = NULL;
 	if (p->bdev_file) {
-		set_blocksize(p->bdev, p->old_block_size);
 		fput(p->bdev_file);
 		p->bdev_file = NULL;
 	}