[RFC 15/23] readahead: align with mapping_min_order in force_page_cache_ra()

[Pankaj Raghav <kernel@pankajraghav.com>]

From: Pankaj Raghav <p.raghav@samsung.com>

Align the index to mapping_min_order in force_page_cache_ra(). This will
ensure that the folios allocated for readahead that are added to the
page cache are aligned to mapping_min_order.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
 mm/readahead.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/readahead.c b/mm/readahead.c
index 2a9e9020b7cf..838dd9ca8dad 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -318,6 +318,8 @@ void force_page_cache_ra(struct readahead_control *ractl,
 	struct file_ra_state *ra = ractl->ra;
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
 	unsigned long max_pages, index;
+	unsigned int folio_order = mapping_min_folio_order(mapping);
+	unsigned int nr_of_pages = (1 << folio_order);
 
 	if (unlikely(!mapping->a_ops->read_folio && !mapping->a_ops->readahead))
 		return;
@@ -327,6 +329,13 @@ void force_page_cache_ra(struct readahead_control *ractl,
 	 * be up to the optimal hardware IO size
 	 */
 	index = readahead_index(ractl);
+	if (folio_order && (index & (nr_of_pages - 1))) {
+		unsigned long old_index = index;
+
+		index = round_down(index, nr_of_pages);
+		nr_to_read += (old_index - index);
+	}
+
 	max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
 	nr_to_read = min_t(unsigned long, nr_to_read, max_pages);
 	while (nr_to_read) {
@@ -335,6 +344,7 @@ void force_page_cache_ra(struct readahead_control *ractl,
 		if (this_chunk > nr_to_read)
 			this_chunk = nr_to_read;
 		ractl->_index = index;
+		VM_BUG_ON(index & (nr_of_pages - 1));
 		do_page_cache_ra(ractl, this_chunk, 0);
 
 		index += this_chunk;
-- 
2.40.1