[PATCH v6 01/11] readahead: rework loop in page_cache_ra_unbounded()

["Pankaj Raghav (Samsung)" <kernel@xxxxxxxxxxxxxxxx>]

From: Hannes Reinecke <hare@xxxxxxx>

Rework the loop in page_cache_ra_unbounded() to advance with
the number of pages in a folio instead of just one page at a time.

Note that the index is incremented by 1 if filemap_add_folio() fails
because the size of the folio we are trying to add is 1 (order 0).

Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
Co-developed-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Acked-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 mm/readahead.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index c1b23989d9ca..75e934a1fd78 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -208,7 +208,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 	struct address_space *mapping = ractl->mapping;
 	unsigned long index = readahead_index(ractl);
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
-	unsigned long i;
+	unsigned long i = 0;
 
 	/*
 	 * Partway through the readahead operation, we will have added
@@ -226,7 +226,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 	/*
 	 * Preallocate as many pages as we will need.
 	 */
-	for (i = 0; i < nr_to_read; i++) {
+	while (i < nr_to_read) {
 		struct folio *folio = xa_load(&mapping->i_pages, index + i);
 		int ret;
 
@@ -240,8 +240,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 			 * not worth getting one just for that.
 			 */
 			read_pages(ractl);
-			ractl->_index++;
-			i = ractl->_index + ractl->_nr_pages - index - 1;
+			ractl->_index += folio_nr_pages(folio);
+			i = ractl->_index + ractl->_nr_pages - index;
 			continue;
 		}
 
@@ -256,13 +256,14 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 				break;
 			read_pages(ractl);
 			ractl->_index++;
-			i = ractl->_index + ractl->_nr_pages - index - 1;
+			i = ractl->_index + ractl->_nr_pages - index;
 			continue;
 		}
 		if (i == nr_to_read - lookahead_size)
 			folio_set_readahead(folio);
 		ractl->_workingset |= folio_test_workingset(folio);
-		ractl->_nr_pages++;
+		ractl->_nr_pages += folio_nr_pages(folio);
+		i += folio_nr_pages(folio);
 	}
 
 	/*
-- 
2.34.1