fs: remove anon_set_page_dirty()

Use __set_page_dirty_no_writeback() instead.  This will set the dirty bit
on the page, which will be used to avoid calling set_page_dirty() in the
future.  It will have no effect on actually writing the page back, as the
pages are not on any LRU lists.

Link: https://lkml.kernel.org/r/20210615162342.1669332-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/libfs.c

@@ -1217,19 +1217,10 @@ void kfree_link(void *p)
 }
 EXPORT_SYMBOL(kfree_link);
 
-/*
- * nop .set_page_dirty method so that people can use .page_mkwrite on
- * anon inodes.
- */
-static int anon_set_page_dirty(struct page *page)
-{
-	return 0;
-};
-
 struct inode *alloc_anon_inode(struct super_block *s)
 {
 	static const struct address_space_operations anon_aops = {
-		.set_page_dirty = anon_set_page_dirty,
+		.set_page_dirty = __set_page_dirty_no_writeback,
 	};
 	struct inode *inode = new_inode_pseudo(s);