writeback: move the folio_prepare_writeback loop out of write_cache_pages()

Move the loop for should-we-write-this-folio to writeback_get_folio.

[[email protected]: fold loop into existing helper instead of a separate one per Jan]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Brian Foster <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: David Howells <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 10 insertions, 8 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3cbe4a7daa35..fc421402f818 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2411,6 +2411,7 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
 {
 	struct folio *folio;
 
+retry:
 	folio = folio_batch_next(&wbc->fbatch);
 	if (!folio) {
 		folio_batch_release(&wbc->fbatch);
@@ -2418,8 +2419,17 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
 		filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
 				wbc_to_tag(wbc), &wbc->fbatch);
 		folio = folio_batch_next(&wbc->fbatch);
+		if (!folio)
+			return NULL;
+	}
+
+	folio_lock(folio);
+	if (unlikely(!folio_prepare_writeback(mapping, wbc, folio))) {
+		folio_unlock(folio);
+		goto retry;
 	}
 
+	trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
 	return folio;
 }
 
@@ -2480,14 +2490,6 @@ int write_cache_pages(struct address_space *mapping,
 		if (!folio)
 			break;
 
-		folio_lock(folio);
-		if (!folio_prepare_writeback(mapping, wbc, folio)) {
-			folio_unlock(folio);
-			continue;
-		}
-
-		trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
-
 		error = writepage(folio, wbc, data);
 		wbc->nr_to_write -= folio_nr_pages(folio);