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

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

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

Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
---
 mm/filemap.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 199c835c68bf..4ee591bc7e71 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2270,10 +2270,11 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 	unsigned long nr;
 	struct folio *folio;
 
-	rcu_read_lock();
+	if (*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;
 		/*
@@ -2281,11 +2282,11 @@ 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;
@@ -2293,29 +2294,27 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 		if (unlikely(folio != xas_reload(&xas)))
 			goto put_folio;
 
-		if (!folio_batch_add(fbatch, folio)) {
-			*start = folio_next_index(folio);
-			goto out;
-		}
+		if (!folio_batch_add(fbatch, folio))
+			break;
+
 		xas_advance(&xas, folio_next_index(folio) - 1);
+		if (xas.xa_index >= end)
+			break;
 		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