mm/writeback: Add folio_start_writeback()

Rename set_page_writeback() to folio_start_writeback() to match
folio_end_writeback().  Do not bother with wrappers that return void;
callers are perfectly capable of ignoring return values.

Add wrappers for set_page_writeback(), set_page_writeback_keepwrite() and
test_set_page_writeback() for compatibililty with existing filesystems.
The main advantage of this patch is getting the statistics right,
although it does eliminate a couple of calls to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>

1 files changed, 6 insertions, 0 deletions

diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 2ccd8f213fc4..10ce5582d869 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -71,3 +71,9 @@ void migrate_page_copy(struct page *newpage, struct page *page)
 }
 EXPORT_SYMBOL(migrate_page_copy);
 #endif
+
+bool set_page_writeback(struct page *page)
+{
+	return folio_start_writeback(page_folio(page));
+}
+EXPORT_SYMBOL(set_page_writeback);