[PATCH 13/19] writeback: Move the folio_prepare_writeback loop out of write_cache_pages()

[Christoph Hellwig <hch@xxxxxx>]

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

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

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
[hch: folded the loop into the existing helper instead of a separate one
      as suggested by Jan Kara]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Acked-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 mm/page-writeback.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ae9f659e6796ac..d170dab07402ce 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2434,6 +2434,7 @@ 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);
@@ -2441,8 +2442,17 @@ 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;
 }
 
@@ -2505,14 +2515,6 @@ int write_cache_pages(struct address_space *mapping,
 	     folio = writeback_get_folio(mapping, wbc)) {
 		unsigned long nr;
 
-		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);
 		nr = folio_nr_pages(folio);
 		wbc->nr_to_write -= nr;
-- 
2.39.2