[PATCH 08/19] writeback: Factor folio_prepare_writeback() out of write_cache_pages()

Christoph Hellwig
2024-01-25T08:58:36Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Reduce write_cache_pages() by about 30 lines; much of it is commentary,
but it all bundles nicely into an obvious function.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
[hch: rename should_writeback_folio to folio_prepare_writeback based on
a comment from Jan Kara]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Dave Chinner <dchinner@redhat.com>
---
mm/page-writeback.c | 61 +++++++++++++++++++++++++--------------------
1 file changed, 34 insertions(+), 27 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 426d929741e46e..cec683c7217d2e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2397,6 +2397,38 @@ static pgoff_t wbc_end(struct writeback_control *wbc)
return wbc->range_end >> PAGE_SHIFT;
}

+static bool folio_prepare_writeback(struct address_space *mapping,
+ struct writeback_control *wbc, struct folio *folio)
+{
+ /*
+ * Folio truncated or invalidated. We can freely skip it then,
+ * even for data integrity operations: the folio has disappeared
+ * concurrently, so there could be no real expectation of this
+ * data integrity operation even if there is now a new, dirty
+ * folio at the same pagecache index.
+ */
+ if (unlikely(folio->mapping != mapping))
+ return false;
+
+ /*
+ * Did somebody else write it for us?
+ */
+ if (!folio_test_dirty(folio))
+ return false;
+
+ if (folio_test_writeback(folio)) {
+ if (wbc->sync_mode == WB_SYNC_NONE)
+ return false;
+ folio_wait_writeback(folio);
+ }
+ BUG_ON(folio_test_writeback(folio));
+
+ if (!folio_clear_dirty_for_io(folio))
+ return false;
+
+ return true;
+}
+
static void writeback_get_batch(struct address_space *mapping,
struct writeback_control *wbc)
{
@@ -2470,38 +2502,13 @@ int write_cache_pages(struct address_space *mapping,
unsigned long nr;

folio_lock(folio);
-
- /*
- * Page truncated or invalidated. We can freely skip it
- * then, even for data integrity operations: the page
- * has disappeared concurrently, so there could be no
- * real expectation of this data integrity operation
- * even if there is now a new, dirty page at the same
- * pagecache address.
- */
- if (unlikely(folio->mapping != mapping)) {
-continue_unlock:
+ if (!folio_prepare_writeback(mapping, wbc, folio)) {
folio_unlock(folio);
continue;
}

- if (!folio_test_dirty(folio)) {
- /* someone wrote it for us */
- goto continue_unlock;
- }
-
- if (folio_test_writeback(folio)) {
- if (wbc->sync_mode != WB_SYNC_NONE)
- folio_wait_writeback(folio);
- else
- goto continue_unlock;
- }
-
- BUG_ON(folio_test_writeback(folio));
- if (!folio_clear_dirty_for_io(folio))
- goto continue_unlock;
-
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