[PATCH v2 2/5] mm/filemap: reduce xarray lookups in filemap_get_folios_contig()

[Chi Zhiling]

From: Chi Zhiling <chizhiling@xxxxxxxxxx>

Apply the same optimization used in filemap_get_read_batch() by moving
the boundary check from the loop condition to before xas_advance(),
avoiding an unnecessary xarray lookup and reducing branches in the fast
path.

Signed-off-by: Chi Zhiling <chizhiling@xxxxxxxxxx>
---
 mm/filemap.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index d54450e529bd..6bc717f205a7 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2258,11 +2258,13 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 	XA_STATE(xas, &mapping->i_pages, *start);
 	unsigned long nr;
 	struct folio *folio;
+	pgoff_t next;
 
-	rcu_read_lock();
+	if (unlikely(*start > end))
+		return 0;
 
-	for (folio = xas_load(&xas); folio && xas.xa_index <= end;
-			folio = xas_next(&xas)) {
+	rcu_read_lock();
+	for (folio = xas_load(&xas); folio; folio = xas_next(&xas)) {
 		if (xas_retry(&xas, folio))
 			continue;
 		/*
@@ -2270,11 +2272,11 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 		 * No current caller is looking for DAX entries.
 		 */
 		if (xa_is_value(folio))
-			goto update_start;
+			break;
 
 		/* If we landed in the middle of a THP, continue at its end. */
 		if (xa_is_sibling(folio))
-			goto update_start;
+			break;
 
 		if (!folio_try_get(folio))
 			goto retry;
@@ -2282,30 +2284,28 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 		if (unlikely(folio != xas_reload(&xas)))
 			goto put_folio;
 
-		if (!folio_batch_add(fbatch, folio)) {
-			nr = folio_nr_pages(folio);
-			*start = folio->index + nr;
-			goto out;
-		}
-		xas_advance(&xas, folio_next_index(folio) - 1);
+		if (!folio_batch_add(fbatch, folio))
+			break;
+
+		next = folio_next_index(folio);
+		if (next > end)
+			break;
+		xas_advance(&xas, next - 1);
 		continue;
+
 put_folio:
 		folio_put(folio);
-
 retry:
 		xas_reset(&xas);
 	}
+	rcu_read_unlock();
 
-update_start:
 	nr = folio_batch_count(fbatch);
-
 	if (nr) {
 		folio = fbatch->folios[nr - 1];
 		*start = folio_next_index(folio);
 	}
-out:
-	rcu_read_unlock();
-	return folio_batch_count(fbatch);
+	return nr;
 }
 EXPORT_SYMBOL(filemap_get_folios_contig);
 
-- 
2.43.0