fs: remove bdev_try_to_free_page callback

After remove the unique user of sop->bdev_try_to_free_page() callback,
we could remove the callback and the corresponding blkdev_releasepage()
at all.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210610112440.3438139-9-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: zhangyi089

fs/block_dev.c

@@ -1733,20 +1733,6 @@ ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 }
 EXPORT_SYMBOL_GPL(blkdev_read_iter);
 
-/*
- * Try to release a page associated with block device when the system
- * is under memory pressure.
- */
-static int blkdev_releasepage(struct page *page, gfp_t wait)
-{
-	struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super;
-
-	if (super && super->s_op->bdev_try_to_free_page)
-		return super->s_op->bdev_try_to_free_page(super, page, wait);
-
-	return try_to_free_buffers(page);
-}
-
 static int blkdev_writepages(struct address_space *mapping,
 			     struct writeback_control *wbc)
 {
@@ -1760,7 +1746,6 @@ static const struct address_space_operations def_blk_aops = {
 	.write_begin	= blkdev_write_begin,
 	.write_end	= blkdev_write_end,
 	.writepages	= blkdev_writepages,
-	.releasepage	= blkdev_releasepage,
 	.direct_IO	= blkdev_direct_IO,
 	.migratepage	= buffer_migrate_page_norefs,
 	.is_dirty_writeback = buffer_check_dirty_writeback,

include/linux/fs.h

@@ -2171,7 +2171,6 @@ struct super_operations {
 	ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
 	struct dquot **(*get_dquots)(struct inode *);
 #endif
-	int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
 	long (*nr_cached_objects)(struct super_block *,
 				  struct shrink_control *);
 	long (*free_cached_objects)(struct super_block *,