[RFC 2/4] filemap: use minimum order while allocating folios

[Pankaj Raghav <p.raghav@xxxxxxxxxxx>]

Add support to filemap and readahead to use the folio order set by
mapping_min_folio_order().

Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 mm/filemap.c   |  9 ++++++---
 mm/readahead.c | 34 ++++++++++++++++++++++++----------
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 3b73101f9f86..9dc8568e9336 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1936,7 +1936,8 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			gfp |= GFP_NOWAIT | __GFP_NOWARN;
 		}
 
-		folio = filemap_alloc_folio(gfp, 0);
+		folio = filemap_alloc_folio(gfp,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
 
@@ -2495,7 +2496,8 @@ static int filemap_create_folio(struct file *file,
 	struct folio *folio;
 	int error;
 
-	folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
+	folio = filemap_alloc_folio(mapping_gfp_mask(mapping),
+				    mapping_min_folio_order(mapping));
 	if (!folio)
 		return -ENOMEM;
 
@@ -3663,7 +3665,8 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 repeat:
 	folio = filemap_get_folio(mapping, index);
 	if (IS_ERR(folio)) {
-		folio = filemap_alloc_folio(gfp, 0);
+		folio = filemap_alloc_folio(gfp,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
 		err = filemap_add_folio(mapping, folio, index, gfp);
diff --git a/mm/readahead.c b/mm/readahead.c
index 47afbca1d122..090b810ddeed 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -245,7 +245,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 			continue;
 		}
 
-		folio = filemap_alloc_folio(gfp_mask, 0);
+		folio = filemap_alloc_folio(gfp_mask,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			break;
 		if (filemap_add_folio(mapping, folio, index + i,
@@ -259,7 +260,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 		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) - 1;
 	}
 
 	/*
@@ -311,6 +313,8 @@ 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;
@@ -320,6 +324,13 @@ 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) {
@@ -795,18 +806,20 @@ void readahead_expand(struct readahead_control *ractl,
 	struct file_ra_state *ra = ractl->ra;
 	pgoff_t new_index, new_nr_pages;
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
+	unsigned min_folio_count = 1U << mapping_min_folio_order(mapping);
 
-	new_index = new_start / PAGE_SIZE;
+	new_index = new_start / (min_folio_count * PAGE_SIZE);
 
 	/* Expand the leading edge downwards */
 	while (ractl->_index > new_index) {
-		unsigned long index = ractl->_index - 1;
+		unsigned long index = ractl->_index - min_folio_count;
 		struct folio *folio = xa_load(&mapping->i_pages, index);
 
 		if (folio && !xa_is_value(folio))
 			return; /* Folio apparently present */
 
-		folio = filemap_alloc_folio(gfp_mask, 0);
+		folio = filemap_alloc_folio(gfp_mask,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			return;
 		if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) {
@@ -818,7 +831,7 @@ void readahead_expand(struct readahead_control *ractl,
 			ractl->_workingset = true;
 			psi_memstall_enter(&ractl->_pflags);
 		}
-		ractl->_nr_pages++;
+		ractl->_nr_pages += folio_nr_pages(folio);
 		ractl->_index = folio->index;
 	}
 
@@ -833,7 +846,8 @@ void readahead_expand(struct readahead_control *ractl,
 		if (folio && !xa_is_value(folio))
 			return; /* Folio apparently present */
 
-		folio = filemap_alloc_folio(gfp_mask, 0);
+		folio = filemap_alloc_folio(gfp_mask,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			return;
 		if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) {
@@ -845,10 +859,10 @@ void readahead_expand(struct readahead_control *ractl,
 			ractl->_workingset = true;
 			psi_memstall_enter(&ractl->_pflags);
 		}
-		ractl->_nr_pages++;
+		ractl->_nr_pages += folio_nr_pages(folio);
 		if (ra) {
-			ra->size++;
-			ra->async_size++;
+			ra->size += folio_nr_pages(folio);
+			ra->async_size += folio_nr_pages(folio);
 		}
 	}
 }
-- 
2.39.2