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.

[hch@lst.de: fold loop into existing helper instead of a separate one per Jan]
Link: https://lkml.kernel.org/r/20240215063649.2164017-13-hch@lst.de
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Dave Chinner <dchinner@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3cbe4a7daa357c9291eeaa48f4d3c13531921358..fc421402f8188179fe1f58f0fc1217ef01c684cc 100644 (file)
--- 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);