[PATCH 12/17] writeback: Factor writeback_iter_init() out of write_cache_pages()

[Christoph Hellwig]

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

Make it return the first folio in the batch so that we can use it
in a typical for() pattern.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 mm/page-writeback.c | 39 ++++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 70f42fd9a95b5d..efcfffa800884d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2442,6 +2442,22 @@ static bool should_writeback_folio(struct address_space *mapping,
 	return true;
 }
 
+static struct folio *writeback_iter_init(struct address_space *mapping,
+		struct writeback_control *wbc)
+{
+	if (wbc->range_cyclic)
+		wbc->index = mapping->writeback_index; /* prev offset */
+	else
+		wbc->index = wbc->range_start >> PAGE_SHIFT;
+
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+		tag_pages_for_writeback(mapping, wbc->index, wbc_end(wbc));
+
+	wbc->err = 0;
+	folio_batch_init(&wbc->fbatch);
+	return writeback_get_next(mapping, wbc);
+}
+
 /**
  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
  * @mapping: address space structure to write
@@ -2477,29 +2493,14 @@ int write_cache_pages(struct address_space *mapping,
 		      struct writeback_control *wbc, writepage_t writepage,
 		      void *data)
 {
+	struct folio *folio;
 	int error;
-	pgoff_t end;		/* Inclusive */
 
-	if (wbc->range_cyclic) {
-		wbc->index = mapping->writeback_index; /* prev offset */
-		end = -1;
-	} else {
-		wbc->index = wbc->range_start >> PAGE_SHIFT;
-		end = wbc->range_end >> PAGE_SHIFT;
-	}
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
-		tag_pages_for_writeback(mapping, wbc->index, end);
-
-	folio_batch_init(&wbc->fbatch);
-	wbc->err = 0;
-
-	for (;;) {
-		struct folio *folio = writeback_get_next(mapping, wbc);
+	for (folio = writeback_iter_init(mapping, wbc);
+	     folio;
+	     folio = writeback_get_next(mapping, wbc)) {
 		unsigned long nr;
 
-		if (!folio)
-			break;
-
 		folio_lock(folio);
 		if (!should_writeback_folio(mapping, wbc, folio)) {
 			folio_unlock(folio);
-- 
2.39.2